yet another surging idle problem!!!

:banghead: ok folks, please HELP!!!! I have a 92 brew 5.7 7r4 trans 16?,??? miles. Have had fuel pump/filter spark plugs replaced iac, air temp, o2 sensores repaleced. tried a new map sensor, and still surging, but just at idle. it surges from 750-1100 rpm. What else can it bee. I've checked for vac. leaks. but have not found any. I replaced the map last, when I was fiddling around, I unplugged the old map sensor and the idle was normal, so i replaced it, but it didn't resolve. I should add that the ac clutch went out, but comp. spins, could that have anything to do with the idle prob??? any info, will be greatly appreciated!!!!

Check the throttle position sensor these will give erratic idle. Watch the voltage on your scanner to check what is happening.

How do you check the tps voltage???

My OTC 4000E will give you the voltage. If you don have a scanner make some connectors and use your DVOM. Or you can use a couple bed of nails leads on your volt ohm meter. These leads have small pin points which penetrate the cable. Use silicon to coat the leads after testing. DVOM digital volt ohm meter.

what causes the idle to be erratic on warm up??? It seems that when the car is warming up it is surging. then after a few minutes it is smooth. When I drive it, it hesitates unless I stand on the gas it takes off after a few seconds.

I would check terminal connections at MAF,idle air control,t-p sensor,
Did you check distributor cap and rotor. If you have a logic probe that checks for pulsating signal,5volt reference,positive,and negative. I would check the connections at the distributor. Also check for any bad hose from the air filter,to the intake. I had to clean the intake on my 5.3L pickup as it was sticky.

Thanks for the replys rhandwor, I have replaced the plugs, after that it was at the state of still surging and close to stalling, so I thought I was on the right track, before the new plugs it would not stay running. I checked the dist. cap and all of the nodes(???) had about an 1/8 of an inch of buildup on them so I changed that and same thing. When I drive the car, it feels like it's missing and when I put it into the passing gear it just seems that there is no power, and feels like it jerks a bit through 30-40mph. Would the plug wires even though they clip on nice and snug cause this? I don't recall ever having a problem with plug wires before. I will try to check voltage on the tps, and this car does not have a maf, but i did change the iat sensor

I used aftermarket plug wires and a lot of them I had to recrimp the ends at the spark plug.
My son's 5.7L in a 1997 GMC pickup started having these type of problems and then the fuel pump falied. When replaced the problems stopped. I would check the pressure with a gage for operating and crimp off the return to check full pump pressure. If you don't have a gage use vise grips and slowly tighten on the return at a rubber hose have some body gun the car and see if it improves.
I would use a spark plug grounded to the frame and check for a good spark.
You also could loosen the exhaust nuts before the catalic converter pull apart appx. 1 inch to check if your converter is plugged.

thanks again for the input. the fuel pump was replaced first. but that did not solve the surging. the fuel pump is about 4 maybe 5 month old. the cat. was replaced last winter, but I was wondering if it may be clogged. I tuned-up only the plug cap and rotor, you think a wire maybe bad? I've been reading some relatively related issues with acceleration, stalling and hard starts and i keep seeing purge canister solinoid, and egr/ egr solenoid could 1 of these cause the surging? and I had the car at a mechanic and he checked the cts voltage and said that it was operating normal. I need to get it tested for emissions, but I know it won't pass. Will the results help in pointing in the right direction?

These vehicles have a fuel dist. with a pressure regulator if you look along the manifold it is cast iron about 2 inchs by 4 inchs. They put the regulator on the inside so you have to remove the upper plenium chamber to replace. If you can pull the vacuum hose with a long needle nose check for fuel in it. This is why I suggested clamping the return hose with needle nose channel locks. If bad the car should have more power. Using a pressure gage is best.
The emissions test will give you all codes. Auto zone will scan your engine for codes free. Walmart sells a scanner for $68.00. I would use an ohm meter to check all plug wires. Was your rotor replaced with the cap.
Pinch off the vacuum hose to the brake vacuum booster they sometimes cause problems. If you have a haynes follow instructions to ohm the coil.
Use a volt meter put 12 volt on the positive the negative should be 11 plus volt. Disconnect the neg when doing this.
Also ohm the temp. sensor if it is over 7000 ohms ohm a new one at a parts store. A grounded unit will cause problems.

I don't have tpi, it is tbi. But i'm going to test the coil and wires. I didn't even think about testing the wires, but I already intened to test the coil, tks!!! I'll try tonight and post back. I'm going to test the car for emissions in the morning realy doubt it will pass, but i'm interested to see the results.

If its throttle body injected you can try to enrich the mixture with starting fluid if it smooths out it is a fuel problem. Gun the engine while spraying if it works a lot better it is a fuel problem. The pressure regulator is under the back of the throttle body. They sell rebuild kits for them. Splice a tee in the fuel line and install a pressure gage.Better buy a pressure gage with a fitting you can screw onto the gage mounting valve. You can use fittings where it screws into the throttle body. A lot of these throttle bodies get dirty and need cleaned out. You can buy a kit like a carb. kit. I have pulled them off and cleaned all openings with carb. cleaner. Auto zones yellow can is a good one.
Gum out is about 30% of what it used to be.
The egr valve on these engines cause a rough idle when leaking. You can get on a hill and the engine shakes. Try plugging the hose to the egr with a small bolt. Also check if its leaking through. Clean it out real good and lube the shaft with spray greese. Use a vacuum gage and check that it gets vacuum when the engine is gunned. Sorry I was thinking you had a newer design engine.

that is ok, I'm just happy to be getting a response. the car has been like this since july.

Maybe this will help, or not. The tempurature here dropped down to low 20's. I didn't get a chance to mess with the car, but I thought I would start it to see how it would react in this cold weather. When it started the idle dropped once right away, but recovered and seemed to run normal cold idle.:screwy: It ran fine for about five minutes then started the surging, but never stalled. What do you make of that.

When the temp drops the fuel mixture is a lot richer. I would get a can of carb. cleaner. Spray around the edges of the intake manifold and around the base of the throttle body. Check pcv valve hoses and other vacuum hoses for leaks. If you have an intake leak the engine will smooth out when the spray hits it. I had a friend with a big motor in a chevy and he went to the junk yard and bought two injectors from a 305. This caused the same problem you have. When starting fluid was sprayed into the throttle body it smoothed right out. He then had to buy two injectors from a 5.7L throttle body.
Try unplugging the temp. sensor and see what happens.

had car tested for emissions, failed hc test by .04 gpm. pulled some codes off I had a 15 which i'm assumeing was the temp sensor that I unplugged and a 44 which came on on my way to the test station. I'm going to pick up a can of carb cleaner and try for a leak today. TKS!

The 15 was the temp.
The 44 is lean exhaust
Make sure the temp. sensor is plugged in when hunting for a vacuum leak.
Also disconnect hose to vacuum booster and put a bolt in it.

O.K. I just saw your post on the booster hose, i will try that tomorrow if I get a chance to mess with it. But, tonight I put new plug wires on it and it had a steady idle but seemed to take long to warm up, so there was a difference at start-up. It still fell on its face when I drove it. It did run alittle better when the car got warmer. I disconnected the temp sensor, and it stayed running, so I drove it and it was much much better. Does that mean the sensor is bad??? and How can you tell if the thermostat is bad?

With the temp. sensor disconnected it should be running very rich not lean.
The only way to check the temp. sensor is to ohm it or check voltage when running. With the sensor disconnected you probably will get 5mpg.The readings vary by the temp. If you ohm it tell me what you get and and the outside temp. Or pull it out and take it to a parts store and compare readings.
If the thermostat is opening fell the top hose when fully hot. Then feel a top hose on another car that is fully warmed up. You can feel the difference.
I really think you have a vacuum leak fix that then worry about other problems.

I tested the temp sensor, it was at 4 almost 5 ohms cold. I put the voltage meter on it. Cold it was just under 4 volts, and dropped gradually to between 1.9 and 1.12 volts. the outside temp was around 28 degrees. I tried checking for a leak, I pulled the vac. First I pinched the hose for the booster and right away it seemed to smooth out, but i think that was coinsidence(not sure). I did end up plugging the booster vac. and spraying the carb cleaner along the manifold but it didn't seem to change anything. I probably didn't do it right. I'm supposed to spray along the manifold and valve cover right? while givinig it throttle. The car runs like crap. It idles smooth when the surging goes away but when I drive it it stumbles. It is weird.

Spray along the sides of the intake manifold where it bolts on and around the base of the throttle body. Spray around any vacuum lines to the throttle body. Does it run better with the bolt in the vacuum line to the brake booster. A leaking break booster will definately cause problems. Also spray around this hose. If you can't find a vacuum leak pull the throttle body and clean out any openings. If you find a leak try to tighten the bolts to the intake or throttle body and recheck. I will check in the morning the ohms but I think they are close. They way you are operating is equalivent to running with the choke stuck closed. So you are getting air somewhere.

I scanned through your posts, so if I missed ae earlier reference to it, pardon me, but you may want to take a look at the EGR system. As rhand is alluding, TBI systems (speed/density) are very sensitive to manifold pressure (vacuum). The power brake booster, EGR, and PCV systems are suspect.

A leaking EGR vacuum solenoid valve or carboned EGR valve pintle can cause your symptoms. Check for this:

http://72.19.213.157/files/EGRValvePintleCarbon262V6W.jpg

Don't forget to pull the brake booster vacuum line and cap it, and check teh PCV valve, vacuum hose, and make sure the PCV valve is the correct one for your engine - They all flow at different rates.

BTW - The CTS/IAT sensor is not right. The resistance should be closer to this:

http://72.19.213.157/files/CTSMAT.gif

tks for the table bb. it does seem that the resistance is a bit low. I'm sure it was close to 4ohms. I'll check it again. How can I clean the EGR valve. I took it off and look inside it, but did not scrape i to see how much carbon was built up inside. Tks!!!

P.S. I'm not sure if I mentioned this in the original post, but the tbi gasket was replaced also in trying to resolve this issue.

His picture is of a newer egr valve. Push up on the vacuum port and clean around the valve with carb cleaner. Take a piece of heater hose and try to blow through the valve. If it leaks get a new one. The throttle body is in two pieces I'm almost sure. Tighten the upper part against the gasket. See if the vacuum diaphram part of the egr valve is leaking if so replace. If its your original pcv clean it out with carb cleaner or replace. Check pcv hose to be sure it isn't plugged.
If your brake booster is leaking get a rebuilt or good used one. Lay a ruler flat over the hole and measure the length. They can be adjusted so write the length down before turning in yours for a core.
What is your mileage on this engine? Do you know how to check timing? If you do can the computer advance the timing?
If over 100,000 and the timing chain hasn't been replaced turn the engine over by hand about 60 degrees past top dead center clockwise. Then turn back counterclock wise to zero degrees. Pull the distributor cap and use white out mark the dist. where the rotor tip is. Have somebody watch as you turn the crank by hand. Stop as soon as the rotor starts to move. Anything over 15 to 20 degrees the timing chain needs replaced.

I took the EGR valve off, and tried cleaning it. didn't have much on it. but I pushed the diaphram till it stopped and plug the vacuum port and the diaphram slowly open. is this normal or is it leaking.

I never checked one this way so I'm not certain. I usually put a vacuum valve on the solenoid valve gun the engine and if I get vacuum, I connect the egr valve gun the engine and if it opens its ok. I also have used a vacuum pump.
What did you decide about the vacuum booster does your engine run better or not.
Does it ever idle good with the temp sensor connected or not? Sometimes a bad knock sensor will retard timing when trying to gun the engine. At this time
exactly what is happening. What is the mileage? Any backfire or does it act like a dead cylinder I've had a worn valve guide that the rocker arm would turn and the engine would miss move back into place and run perfect. I found this with the valve cover removed and I could move the valve spring. I found the correct cylinder by doing a compression test. I've also had a cracked plug.
Does this happen all the time or is it hit and miss?

Just for s@#ts and giggles, the ohms on the cts were 9600@25f

Well about the EGR, I did try to move the diaphram while the car was running, and when I did it sounded like it was going to stall. So may be it is o.k.

Does it ever idle good with the temp sensor connected or not? The idle seems fine at first until it starts to warm up then it starts to sruge up and down between 500 and 1000rpm. It seems when the car is at normal temp it smooths out for a few mins then surges a little bit, then smooths out and so on. The car when it idles normal it is really smooth. The odometer does not track properly, so the car may have close to 200,000 on it i'm not sure. I'm going by the service records that came with the car. Although when I drive the car it is the same thing everytime. it stumbles from a dead stop if I give it close to ful throttle. If I give it 1/4 to 1/2 throttle it seems better but not fuul power. Sometimes when I hit the throttle at around 25mph it hesitates for a second or 2 and then takes off but jerks until it shifts, sometimes it is smooth, but does not feel like ful power.


I have not tried the booster again. I need to put the EGR valve back on and stuff. I will try it again after that. It does seem like the brake pedal is a bit stiff when I brake. I will pay more attention to that if I drive it again.

Before you install the egr look at the bottom I had a truck I worked on with a new egr but they didn't put the spacer washer in it. Aftermarket egr's have a washer with the proper calibration so it will fit many vehicles. So when this valve opened it pulled to much flow and the engine shook. This is one thing I would check before I put it on.

there was no spacer on the EGR valve. I will try to post a pic of the EGR valve.

Orginal equipment egr valves don't have a spacer. Just some aftermarket valves.

Whatevr happened to testing the TPS.. any conclusive results? The MAP was replaced, but was that system vac checked?

I only have a dmm. I don't have a scanner to test the tps. I should be able to us the dmm though. I just need to figure out how to measure it.

What ever happened did you ever get the problem fixed?

I only have a dmm. I don't have a scanner to test the tps. I should be able to us the dmm though. I just need to figure out how to measure it.

If your interested, i could tell you exactly how to test the TPS with your multimeter. Let me know.

rhandwor, no I'm still having problems. (Although, it did pass emissions)I cleaned the egr, but it wasn't bad at all. Still not sure if it is leaking though. I need to find my vac tester. I do notice the temp gauge does not stay at 195*. I keep getting code 44, I was told that the ecm is sensing a rich condition, and is leaning it self out. I did read that the thermostat can cause a lean condition, but I'm not convinced on that. I do think it has somehthing to do with the timing. I did advance it a bit, and the car doesn't jerk as hard when I floor it. It still surges with a steady throttle in the 30-45mph range. I'm going to try to test the tps. At the same time I'm going to move the crank back and forth by hand to see how much play there is. I did notice that the chattering from the engine is not as noticable now. before it would chatter pretty consistently, but I have hardly noticed it now. I found a procedure on how to check the tps, but wasn't sure if it was right. This is what I found.

Throttle Position Sensor - Testing

Set DMM to read DC Volts.

Connect black COM lead probe tip to the TPS ground wire.

Connect red Volts lead probe tip to the TPS Reference Voltage wire.

Turn ignition ON. Do NOT start engine.

Look for a 5 volt reading - (some manufacturers may differ - verify correct reference voltage for the specific vehicle being tested).

If reference voltage is too high or too low, look for a problem with the wiring harness or PCM.

After establishing reference voltage is O.K., connect the red Volts lead probe tip to the TPS to PCM signal return wire.

Look for low voltage at idle position that will smoothly increase as throttle is applied. Any fluctuation of the DMM Bar Graph or erratic voltage readout indicates a bad sensor. Verify factory specs for low voltage (idle) setting, even one tenth off can make a difference in vehicle performance. The high (full throttle) voltage should reach at least 80% of the reference voltage.

Turn ignition OFF when test is complete.


If you guys can let me know if this is accurate I would appreciate it. And if it is do you know the specs I should be reading?

rhandwor, no I'm still having problems. (Although, it did pass emissions)I cleaned the egr, but it wasn't bad at all. Still not sure if it is leaking though. I need to find my vac tester. I do notice the temp gauge does not stay at 195*. I keep getting code 44, I was told that the ecm is sensing a rich condition, and is leaning it self out. I did read that the thermostat can cause a lean condition, but I'm not convinced on that. I do think it has somehthing to do with the timing. I did advance it a bit, and the car doesn't jerk as hard when I floor it. It still surges with a steady throttle in the 30-45mph range. I'm going to try to test the tps. At the same time I'm going to move the crank back and forth by hand to see how much play there is. I did notice that the chattering from the engine is not as noticable now. before it would chatter pretty consistently, but I have hardly noticed it now. I found a procedure on how to check the tps, but wasn't sure if it was right. This is what I found.

Throttle Position Sensor - Testing

Set DMM to read DC Volts.

Connect black COM lead probe tip to the TPS ground wire.

Connect red Volts lead probe tip to the TPS Reference Voltage wire.

Turn ignition ON. Do NOT start engine.

Look for a 5 volt reading - (some manufacturers may differ - verify correct reference voltage for the specific vehicle being tested).

If reference voltage is too high or too low, look for a problem with the wiring harness or PCM.

After establishing reference voltage is O.K., connect the red Volts lead probe tip to the TPS to PCM signal return wire.

Look for low voltage at idle position that will smoothly increase as throttle is applied. Any fluctuation of the DMM Bar Graph or erratic voltage readout indicates a bad sensor. Verify factory specs for low voltage (idle) setting, even one tenth off can make a difference in vehicle performance. The high (full throttle) voltage should reach at least 80% of the reference voltage.

Turn ignition OFF when test is complete.


If you guys can let me know if this is accurate I would appreciate it. And if it is do you know the specs I should be reading?

That procedure is right on the money. Low signal voltage to expect would be from .45v to 1v. High signal will be about 4v to 4.75v.

With your mileage and having to move the timing is a sure sign of a loose timing chain. I think it is stretched about 60 degrees and the computer keeps hunting finds a good spot then the timing changes moving the rpm up and down.
A new two piece timing set and gasket & seal with a readi sleeve is what the engine needs. 200,000 on the original set it is way past time. The parts will be cheaper than a tow home. Rent a propane heater for the garage and find a good warm day. You should be able to do this in one day.

How many miles is the timing set in this engine good for? and when I move the timing mark to see how many * it is off how can I tell for sure how many it is off by. I've only set the mark to factory before, but never payed attn to the marks. how is that read. I'm going to do the mark on the dist. also. I've come across some info on changing the iac. mentioned that you need to compare the old and new and set the new to the old. I just swapped it out, never payed attn to the two together. they both looked identicle. Is that somthing you need to do when swapping the iac?

Normally they were towed in around 150000 when I had a garage. The gear for the camshaft had a plastic coating and it wears and they either break off or it will jump a tooth. I may have had one towed in around 198000 to 205000 but I don't remember exactly.
Turn the dist. clockwise about 60 degrees past top dead center. Then turn it counter clockwise to top dead center. Pull the dist. cap use white out and mark where the rotor tip is above the dist case.
Have somebody watch the rotor as you turn the engine clockwise by hand with a ratchet when it just starts to move stop. Look at the timing mark on
the engine this will tell how much it is stretched.
If yours has never been changed and it is original equipment your are on borrowed time.

Does it matter where I get the timing set, what would you recomend??? Also, we've been driving the car they way it is, and I noticed that when I give it alot of gas, the heat when it is directed to the floor starts comming out of the vents until I let off the gas. I just noticed that. Was just curious.

I would just go to Advance Auto or Auto Zone I think they use TRW sets.
I think the vacuum drops when you floor it and with the age on the car you have some small vacuum leaks.

I found my vac. tester, what reading , or readings should I find. and do I need to test in different locs, ar just one.

Try to find a port on the intake manifold. Check it at idle and when gunning the engine. Also use a long hose and check the vacuum on the road. List the readings and we will try to interpret what you are getting. Be aware that timing affects the readings. Be sure to state if steady or fluxating.

I've been really busy lately, haven't had a chance to check vac. Just curious, will i have to remove the oil pan to change the timing set, or can I just drop it and reuse oil pan gasket?

I just loosened the bolts on the front part of the pan then I was able to remove the timing cover. You might to pry a little. The new timing cover comes with a new gasket.
I used silicon at the bottom corners to prevent leakage and tried to get some under the edge between the pan and gasket. This assumes you have the old type of gasket not the new formed rubber gasket.

I've been soooooooo busy, but i have been tinkering with the car this past week and I tried starting fluid along the manifold and seems to raise the rpms if I spray a lot of fluid on the pass. side. I also sprayed along the driverside exhaust manifold and also seemed to make a slight difference. but wasnt sure if the fumes from the spray are strong enough to cause a difference if they were sucked into the tb, while sprayng on dr side. I also test drove the car with the egr disconected and egr vac. hose plugged. The car when I used the passing gear was really smooth. it hardly jerked like it did b4. Would that point to egr or egr solinoid?

O.K. I checked again for a leak on the manifold before I went and bought the gaskets, and now it seemd not to have an effect on the idle. I am leaning towards the egr valve so I ordered one, we'll see what happesns.

update: I ordered and replaced the egr valve. seemed to make a big diference, but still surging at idle when cold, or when the car has been off for 30 mins up to 3 hrs. and slight surge at about 45-50 mph, but not nearly as bad. I found the driverside manifold bolts were loose, that is probablyt why I kept getting DTC44 every time we drove the car. now it comes on periodically. I'm going to remove all vac ines and closely inspect them also, r&r the timing set, as rhandwor suggested. Does seems like there is a sweet spot in the ignition system. sometimes she runs pretty well, then she don't, weird!

few, back to trying to figure this out. the only thing i had not been able to replace is the timing set. There is quite abit of slack in the chain. I can move the crank back and forth a good 1/2". Will timing throw off the vacuum. I put a vac gauge on it, and it was pretty steady at 19". Then after about 2mins, it went up and down from 20-15. followed same pattern as idle. I want to put a fp tester t figured out how to make a schrader valve.

Timing does affect the vacuum. Its plenty warm buy a two piece timing set unless the bottom gear is worn then get a 3 piece set. Normally a two piece set is all you need. You have spent about as much time checking as it would take to do the job. Do it in a garage or where you have plenty of shade. A good weekend job. I use a short mechanics rule when I set the two marks for the timing chain the two marks one on top and one on the bottom. They are closest together at this point. Do this before spending a lot of time. While not normal I had a customers 350 bend a valve when his chain broke possible just burnt valve. I just installed a long block but he didn't have compression in one cylinder and he wanted a long block after installing a chain and the other problem showed up.
Look at a flea market for a shrader valve where you can cut and splice the hose.
I always found if you repair known problems first this normally fixes the problem.

I can find a schrader valve at the flea market!? Never thought of that. So I was thinking to just cut a section out of the fue line and for reading purposes only connect my homemade schrader in place of the section I cut out. Then I could just replace it with fuel hose and clamps, that should be o.k.

Oh, welcome back!

You can remove the valve stem and use a couple different size of hose to check pressure. Just replace the valve stem when done. From past reply's you have plenty of fuel. Just fix the timing if you still have a problem then do further checking.

How about an update did you ever get it fixed. It is getting cool enough to work on the car.

no update yet, we have 2 cars, the wagon and an alero. the alero needed bearings, had to replace 1 of the 2 twice. so that took up my past 2 weekends. I have found a timing set at az for 80bucks. I probably will pick it up this week and start on the weekend. I did remove the ign. module and it had green/white prongs on the connector that is inside the cap. cleaned the contacts and seemed to drive better under load, but the car just won't stay running if I set the timing to 0* before tdc. I have to advance the timing to where the timing mark is about 2-3 inches left of entire timing mark.

They sure went up in price as I used to get them for around $25.00.

well I went to AZ on sat. to p/u timing set, and they were out of stock and wouldn't have any in till wed. So I didn't get to replace it. I do have it apart, and i read a previous post and it stated that the new cover came with gasket. Do I need to buy a new timing chain cover. Can't I just use the old one? And will I need a gear puller for crank gear?

You don't need a new cover unless it is damaged leaking oil or bent. I normally just inspected the lower gear and replaced if it was defective. I normally bought two piece sets. A puller is needed to remove the lower gear. Advance Auto and Auto Zone loan tools if you buy parts from them. You could borrow a puller from a friend.

So made some progress. last i left the car with just the timing cover to be pulled off. I pulled the cover off this morning to find that it does have a all steel cam gear. I have the marks lined up and there seems to me that there is a bit of slack in the chain. I'm no mechanic, but to me it seems to have some slack. But now since it looks like it has been replaced, I'm not to sure. I remember when I was checking timing, the mark would jump to the left alot, 1 maybe 2 times every 30 sec. I had to watch it a few times to find out where it was moving to. So that was when I started leaning towards timing chain. but now since the gear is not the plastic coated factory gear, now i'm wondering if it would be something electrical causing the jump in the timing mark. Well, since I do have the front apart, I will change the chain, and the gear. now should I just drop a whole new set in or just go with the cam and chain?

still need to finish installing timing cover etc. etc. etc. But all in all it is going smooth