Low/searching Idle and stalling

My 97 Blazer 4.3 has just developed a stalling problem only when coming to a stop. It starts fine and seems to run fine at speed. When I start it cold the idle is around 1000RPM then it warms up and the idle gets down to about 650RPM(seems a little low?), at which time the tach seems to "search" for the right idle - up50-100RPM, then down 50-100RPM. It has not stalled in the garage, just on the road. Here is what I have done:
New PCV
Checked IAC (per Chilton) and cleaned
Checked MAF(just for voltage to the plug - can't check frequency of pulsed till I bring home freq meter)
Checked Air Temp Sensor.
Checked TPS(per manual)
Just now took out EGR (cleaned, little valve with star screw seems sticky when I press on it, how do I clean this - is it OK to soak? No diaghrams to erode?)
Checked vacuum hoses I can see? Probably a bunch more?

Plugs are 1 year new.
Fuel filter is ~15months new (I hated changing that b*tch)
Fuel pump is whiny - but always has been - no problem when I get on it?
Bad gas? Should I try to run the 1/4 tank empty and put fuel treatment of some sort?

Any ideas would be appreciated - a bunch.
-Shawn

Put the (cleaned?) EGR back in - same problem.

I am going to put on new wires/cap/rotor, then trying fuel filter, then gas treatment - off to Autozone.

-Shawn

Tried plug and coil wires, rotor and cap. Man I almost blew a human gasket trying to put new wires on the crazy truck. I can't believe they would engineer those wires retainers/seperators so that you had to almost cut 'em off. Stupid. Anyhow, no help. It seemed to be running fine when I first started it and then for no reason, not even a low or rough dle it just stalled flat out. No codes- all the normal lights. Started right up. Then the idle creeped low and got that searching low idle again. Fuel filter tomorrow, then maybe take it to the shop for fuel pump and expert diagnosis next is all I can think of. I am taking a break from her today.

I changed the fuel filter - no help. It still idles low and searches for an RPM up and down(only about 50RPMs).
-Shawn

I did some more work as follows:
1)Finished checking MAF using frquency meter - seems to work as required.
2)Checked fuel pressure - read 65PSI during 2sec start, then dropped to ~56-58. Started it, and it stayed at ~56PSI.
3)Drained most of gas, refilled with 91, then added some Berrymans gas treatment.
All this and it still idles low and sounds like it may stall soon.

4) Finally, I unplugged the O2 sensor to se if I could get the engine computer to go to defaults, in case O2 was marginal - still ran bad, but guess what. I did not get an SES light - should I? Is the O2 bad or what?

I must be talking to myself here - or have really got a stumper - I have no replies except to myself?

Any help at all would be appreciated.

-Shawn

Hi! I have a '94 Blazer S10, which had become a total & complete nightmare in the past year or so. I've had the truck less than 3 years. I'm not sure if this will help or not, but have you tried the Idle Air Control? I had the same problem just a few months back - and am having it again now.

After being without a car for nearly 2 weeks, I got the Blazer back from my mechanic. It was only running rough, but when I got it back, the stalling began AND it still ran rough. So another week with a 2nd mechanic came to the conclusion that it was the Idle Air Control. So, after replacing that, the distributor, spark plugs, and ignition rotor, the truck ran great (grand total of nearly $700 in repairs in less than a month)! I was told that I may need to replace the wires eventually because there was still a bit of misfiring here & there. But, it was running and I was happy.

Now, just a few months later, I'm back to the same problem again. I have a friend with a Blazer of the same year who also had similar problems. He pulled off the Catallytic Converter and that seemed to keep it from stalling, although it does seem to run a bit louder. Who cares? At least it's running!

This is my 2nd Chevy. First was a Camaro. My brother has a Camaro now that has one problem after another - just like I did. I will NEVER own another Chevy! I'm gonna convert to a Ford Girl, or either go back to Nissan! The repairs are expensive, but at least you don't have them every other month!

Hope this helps! Good luck!

Not talking to yourself, just got us stumped too. Try unplugging the MAF unit entirely. Will run ok with a SES light on. If this fixes it you know that's the problem. Next make a solid gasket for the EGR valve and try that. Again will set light but it should run fine. If that fixes it, there it is. Listen real close around throttle body for vacuum leak, bad gasket? If all else fails get it scanned somewhere and see what is erratic.

Thanks for the responses. I have had Fords and Chevys and Dodges - all cars suck to some degree - some worse than others - but you gotta have 'em.

The IAC seems to check out - the resistances are in tolerance. Tom3 - I tried that with the MAF and it did not work. I thought about the EGR plate because I have heard so much about their troubles - I just have not gotten around to making a plate. Guess I better try that before much else. I guess a "scan" can show things even if SES is not on? Is that the same OBD2 tool Autozone will use for free - or is there a more in depth check a mechanic could do?

Thanks,
Shawn

Not sure what Azone uses. There are code pullers and then scanners that will watch each sensor's output. Can watch for an erratic reading and such.

Rough, Unstable, or Incorrect Idle and Stalling
Checks
Action

Definition: The engine runs unevenly at idle. If severe enough, the engine or vehicle may shake. The engine idle speed may vary in RPM. Either condition may be severe enough to stall the engine.

Preliminary Check
Refer to Important Preliminary Checks .

Sensor Checks
Check the Heated Oxygen Sensor (HO2S). Check for silicon contamination from fuel or improperly used sealant. The sensor will have a white powdery coating. The sensor will result in a high but false signal voltage (rich exhaust indication). The Control Module will reduce the amount of fuel delivered to the engine causing a sever driveability problem. Refer to the following items
DTC P0131 HO2S Circuit Low Voltage Sensor 1
DTC P0132 HO2S Circuit High Voltage Sensor 1
DTC P0133 HO2S Slow Response Sensor 1
DTC P0134 HO2S Circuit Insufficient Activity Sensor 1
DTC P0137 HO2S Circuit Low Voltage Sensor 2
DTC P0138 HO2S Circuit High Voltage Sensor 2
DTC P0140 HO2S Circuit Insufficient Activity Sensor 2
DTC P0141 HO2S Heater Performance Sensor 2 .
Check the Throttle Position (TP) sensor. If a sticking throttle shaft or binding linkage causes a high TP sensor open throttle indication, the Control Module will not control the idle. Monitor the TP sensor voltage. A scan tool and/or voltmeter should read less than .85 volts with the throttle closed.
Check the Engine Coolant Temperature (ECT) sensor using the scan tool to compare the engine coolant temperature with the ambient air temperature on a cold engine. If the coolant temperature reading is more than 5 degrees greater than or less than the ambient air temperature on a cold engine, check for a high resistance in the coolant sensor circuit or the sensor itself. Refer to the following items:
DTC P0118 Engine Coolant Temperature (ECT) Sensor Circuit High Voltage for the Diagnostic Aids
DTC P0125 Engine Coolant Temperature (ECT) Insufficient for Closed Loop Fuel Control for the Diagnostic Aids
Check the Manifold Absolute Pressure (MAP) sensor response and accuracy.

Fuel System Checks
Check to determine if a Rich or Lean system causes the condition. Drive the vehicle at the speed of the complaint. Monitoring the Fuel Trim will help identify the problem.
Lean - The Long Term Fuel Trim is greater than 150. Refer to DTC P0132 HO2S Circuit High Voltage Sensor 1 for the Diagnostic Aids. Refer to DTC P0137 HO2S Circuit Low Voltage Sensor 2 for the Diagnostic Aids.
Rich - The Long Term Fuel Trim is less than 115. Refer to DTC P0131 HO2S Circuit Low Voltage Sensor 1 for the Diagnostic Aids. Refer to DTC P0137 HO2S Circuit Low Voltage Sensor 2 for the Diagnostics Aids.
Check the fuel injector driver circuit.
Disconnect the injector harness connector at the injectors.
Connect an injector test light between the terminals of each injector connector and note the light while cranking.
If the test light fails to blink at any connector, it is a faulty injector drive circuit harness, connector, or terminal.
Perform the fuel injector coil test. Refer to Fuel Injector Coil Test .
Perform the fuel injector balance test. Refer to Fuel Injector Balance Test .
Check the Evaporative Emission (EVAP) control system. Refer to Evaporative Emission (EVAP) Control System Diagnosis .
Perform a cylinder compression test. Refer to Engine Mechanical.
Check for leaking fuel injectors.
Check the fuel pressure. Refer to Fuel System Pressure Test .

Ignition System Checks
Check the ignition output voltage using the spark tester J 26792 or the equivalent. Refer to Enhanced Ignition System Diagnosis (Overview) .
Check the spark plugs.
Remove the spark plugs.
Check for the following conditions:
Wet plugs
Cracks
Wear
Improper gap
Burned electrodes
Blistered insulators
Heavy deposits
Check the spark plug wires by connecting an ohmmeter to the ends of each wire in question. If the meter reads over 30,000 ohms, replace the wires.

Additional Checks
Check for vacuum leaks. Vacuum leaks can cause a higher than normal idle and low Idle Air Control (IAC) counts.
Check the IAC operation. Refer to the following items:
DTC P0506 Idle Speed Low
DTC P0507 Idle Speed High
DTC P1509 Idle Speed High - Idle Air Control (IAC) System Not Responding
Fuel System Diagnosis
Check the Control Module grounds for being clean, tight, and in their proper locations. Refer to Component Locations in the General Information section.
Check the Transmission Range (TR) pressure switch assembly operation. Refer to Transmission Fluid Pressure Switch Assembly.
Check the scan tool to determine if the Control Module is receiving an A/C signal. Refer to Air Conditioning (A/C) Compressor Clutch Control Diagnosis . If a problem exists with the A/C ON, check the A/C system operation. Refer to Section 1B of the appropriate service manual.
Check for the EGR being ON while idling which will cause roughness, stalling, and hard starting. Refer to Exhaust Gas Recirculation (EGR) System Diagnosis .
Check the battery cables and ground straps. They should be clean and secure. Erratic voltage will cause the IAC to change its position resulting in poor idle quality.
Check the IAC Valve. The IAC will not move if the system voltage is not within 9 to 16 volts.
Check the A/C refrigerant pressure for being too high or for a faulty high pressure switch.
Check the Crankcase Ventilation Valve for proper operation by placing a finger over the inlet hole in the valve end several times. The valve should snap back. If not, replace the valve. Refer to Crankcase Ventilation System .

Engine Mechanical Check
Check for the following:

Broken motor mounts.
Improper valve timing
Low compression
Bent pushrods
Worn rocker arms
Broken or weak valve springs.
Worn camshaft lobes
Refer to Engine Mechanical.


ENGINE ROUGH, MISS & OXYGEN SENSOR DTCS #77-65-12 - (03/13/1997)
SUBJECT: ENGINE ROUGH, MISS, AND OXYGEN SENSOR DTCS (REPLACE OXYGEN SENSOR JUMPER HARNESS)

MODELS: 1996-97 CHEVROLET AND GMC S/T TRUCKS 1996-97 OLDSMOBILE BRAVADA 1997 ISUZU WITH 4.3L V6 ENGINES (VINS W, X - RPOS L35, LF6)

CONDITION:

SOME OWNERS MAY COMMENT ABOUT AN ENGINE MISS AND/OR ROUGHNESS AND A SES LIGHT.

CAUSE:

SOME OXYGEN SENSORS ON THE PASSENGER SIDE OF THE VEHICLE HAVE BEEN FOUND TO BE DAMAGED DUE TO WATER INTRUSION. IF ANY OXYGEN SENSOR RELATED DTC IS STORED, MOISTURE MAY HAVE ENTERED THE JUMPER HARNESS THAT CONNECTS THE THREE PASSENGER SIDE OXYGEN SENSORS TO THE MAIN ENGINE HARNESS AND DAMAGE THE SENSOR AND THE HARNESS. OXYGEN SENSORS THAT HAVE BEEN DAMAGED BY WATER WILL HAVE CORROSION ON ONE OR MORE OF THE SENSORS (4) TERMINALS. THE JUMPER HARNESS CONNECTOR AT THE SAME LOCATION MAY OR MAY NOT SHOW SIMILAR CORROSION. IF THERE IS UNDETECTED MOISTURE IN THE JUMPER HARNESS, A REPLACEMENT OXYGEN SENSOR CAN BE DAMAGED RESULTING IN A REPEAT FAILURE. IN ADDITION, A REPLACEMENT OXYGEN SENSOR MAY BE MISDIAGNOSED AS FAULTY WHEN THE ACTUAL FAULT IS UNDETECTED MOISTURE IN THE JUMPER HARNESS.

CORRECTION:

1. FOLLOW THE STRATEGY BASED DIAGNOSTICS AND PUBLISHED PROCEDURES FOR THE SPECIFIC SYMPTOM AND DTC. 2. INSPECT THE OXYGEN SENSOR CONNECTORS FOR SIGNS OF MOISTURE OR "BLUISH-GREEN" CORROSION ON THE CONTACTS AND IN THE CONNECTOR CAVITIES. 3. IF WATER INTRUSION IS SUSPECTED, BUT NO CORROSION IS EVIDENT, SENSOR FUNCTION MAY BE CHECKED USING A DVOM TO MEASURE RESISTANCE ACROSS THE SENSOR'S PURPLE AND TAN CONTACTS. A DEFECTIVE SENSOR WILL SHOW A RESISTANCE VALUE. A GOOD SENSOR WILL SHOW NO CONTINUITY (INFINITE RESISTANCE) OR "OPEN". 4. IF THESE SIGNS ARE DETECTED, REPLACE THE OXYGEN SENSOR JUMPER HARNESS AND ALL AFFECTED OXYGEN SENSOR(S). DO NOT ATTEMPT TO REPAIR THE JUMPER HARNESS BY CLEANING OR REPLACEMENT OF CORRODED TERMINALS. DO NOT USE OR APPLY ANY TYPE OF SEALANT ANYWHERE IN THE OXYGEN SENSOR CONNECTORS OR WIRES. REPAIR ATTEMPTS TO OXYGEN SENSOR HARNESSES GENERALLY RESULT IN A REPEAT FAILURE.

Wew. Thanks Merlin - I should be able to take care of that list in the next couple minutes. No, really I appreciate all the information - this is exactly what I needed. I bought code reader so I can atleast see any codes thrown that may not have lit the SES - right in my garage too! I will let yall know how it goes after tonight.

Thanks a bunch,
Shawn

Ihad no codes stored according to the reader I bought. I tried new IAC Valve - no help. I unplugged all O2 sensors, no code was thrown, thought I was on to something it seemed to idle nicley, but dropped to 650 again. I tried to adjust idle screw, seemed to hewp, but when I put in gear the idle drops and it feels like it is going to stall - I adjusted idle with it in gear - it just wants to drive fast by itself - thats a bandaid.

Check this out though - I am worried about the water (a good bit) the continues to flow from my exhaust. It is clear (no DexCool). The truck stinks, almost like electrical - the water too. Do I have head gasket problems?

-Shawn

Well - I took it to Casa Chevrolet here in ABQ, NM and got a $87 wash job. Atleast the truck is clean. They could not get it to stall and did not beleive I had a problem. They did not look at it as critical as me a I suppose. Two days later it stalled on my wife. Now I am taking it to a private mechanic - he suggested driving it around with a fuel gauge taped to the window. I went a little too fast with the hood not latched and buckled my hood - this is really pissin me off. Now I probably just doubled my repair bill. What a bonehead! Anyhow, I also removed O2 sensor upstream from the catalytic to check for a clog - no help. One more post - God willing - on the final fix and cost of this whole mess - maybe someone will benefit from my $$$ and experience.

-Shawn

Mechanic says maybe its the fuel pump. He cannot gaurantee that is the problem, but he has done many GMs before. Mine wines then gets quiet then wines very loud again. He verified my other checks were OK. He is sure idle is fine - these things can idle low and still run - the 600-650RPM, is right were the computer wants it according to his scan tool.....so.....tired of greasy fingers, busted knuckels and endless frustration I gave him the go ahead to change it....reluctantly. Pump assy is $540(retail - wink,wink ). In reality I know the assy is $390(for him) - but thats how the game is played. Labor about $200. So, how does $740 sound. Sounded high to me, but what'ya do. It still may not solve it. Grease me up. Ouch!

hi has any one thought to check the knock sensor these do not show up in the scans and control spark advance there are tests avail for these.my 5.7l gmc (p.o.s.) was running like a bag of crap the iac was very lazy,but it started to work better with new exhaust flange gaskets the knock must have transmitted through the engine the truck still isn't 100% but its much better.

How do you test it?

hi disconnect the dark blue wire from the sensor (it's around the oil pan gasket depending on the year either near the oil filter or the starter its round & looks like an oilpressure sender)it has a 100k ohm resister in it measure res between the terminal on the sensor & the block it should be 1.5k to 10k (88 to95)and 90k to 110k ohms(96 to 00) to check it when running hook it up and thump the engine block with a SOFT hammer the idle should change the other test is to probe the wire with the neg meter lead and check for ac voltage it will increase as the engine speeds up if not its hooped. info from a haynes manual#24065 . another thing to check is the star shaped pickup under the rotor buton the distributor shaft will come apart spining the star & messing up the timing .good luck jj.

Thanks hfx - I will ask give this idea to the mechanic. Shouldn't it throw a code?


Shawn

The saga continues - the fuel pump was apparently not the problem. It has been stalling on my wife a week later. It was running good for a week. She said the air bag light has been interrmittantly coming on and off. It flashed when she was moving froma stop and she said it sputtered a bit. It stalled when putting it into gear hours later after having been off. Once it was hard to start. It is hard to diagnose this b*tch. It is back at the mechanic - I am out of ideas and tired of this. I hope he finds something. Any ideas from out there?


Shawn

hi my 94 gmc is a complete bag of shi* last night i changed the wires cap & rotor the distributor shaft broke under the rotor button there is a star wheel it should be affixed solidly to the shaft these DO break and move on the shaft if they spin your timing will move and cause the truck to sh** the bed, put a flat screw driver near one of the points and tap it gently its cast&a magnet it should not move if it spins its hooped and must be changed the gm dealer sells the shaft seperate from the dist and is $95 cdn. this is what i must pick today.good luck jj. (the knock will not set a code in my p.o.s.)

try to hook up a fuel press gauge , then turn the key on ,wait until the pump stops, about 3 or 4 seconds, if it holds press there are no leaks, but if the press goes down in just a second or two one of the cheap,built in failure mode GM plastic pieces of junk fuel lines inside the intake plenumn may have sprung a leak like mine did. Tom

Thanks. Did yours have symptoms like mine?

Mine would start good only if it sat for a couple days, or if I restarted it after sitting only about 5 minutes or less. Otherwise it was always very hard to start (cranked for about 10 seconds). When it did start it ran pretty smooth for about 1 minute, then it would start to miss, and the idle speed was low, and sometimes hunting arround. I disconnected the battery then took off the top plenum and turned on the key on then touched the neg battery term so the fuel pump would run, BE CAREFUL , A GOOD WAY TO CATCH YOU AND YOUR CAR ,GARAGE ,ETC. ON FIRE. got a flash light to look for leaks. don't use a drop light if the gas hits the bulb it could pop and start a fire!! I immediately saw the leak. The repair kit is a GM item acdelco part no. 17112705, costs $44 from rockauto.com, However it is a pain in the butt to change . GOOD LUCK, Tom

I am having the EXACT same problem with a 93 Suburban with 350 engine. I have so far eliminated TPS, IAC, O2 sensor, loose rotor cap or rotor, wires, plugs, walking cam, vacuum leaks, PCV valve, timing, and fuel pressure. I believe I am down to MAP, EGR valve, or computer. I plan on doing EGR and possibly MAP sensor tomorrow. I'll let you know if either works.

I see that this thread is about 4 years old, but I am having the same problem described by sleslie17 with my full-size 1991 GMC Jimmy (same as Blazer) with a 5.7 litre V8.

Does anybody know if sleslie17 ever got a resolution?

I always warm the engine to 100 degress plus before I drive, and it runs perfectly until it gets hot (operating temperature). I can general drive 2-5 miles before it starts acting up...with the low and bouncing/searching idle, such that it feels like the engine going to die.

Once the engine is at it's hottest, the stumbling also occurs during decelleration from about 30mph down to zero.

The carburetor has been cleaned many times, and the engine has had a Motorvac service.

So far I have already replaced the following parts with no improvement:

Tune-Up (GM cap, GM rotor, AC Delco plugs, GM wires)
ECM (computer chip)
Distributor Module
IAC and gasket (this is the only part that isn't available from GM)
TPS (Throttle Position Sensor)
EGR Valve and gasket
MAP Sensor
Knock Sensor
TBI Injectors

I've read in the Haynes books that if the temperature sensor is bad (not the temperature sender), that nothing in the injection system will work properly, so the next thing I'm going to try is replacing the Temperator Sensor, once it comes in (the 4x4 version of the GM part was only available on special order). I also have a GM O2 sensor to try after that.

I've had trouble finding the correct EGR solenoid, but have thought that may be a possibility too.

Other thoughts I've had include replacing the distributor, or even the thermostat (I'm running a 180 rather than the factory 190, but I've been running a 180 for the last 14 years I've owned the truck). I have even considered that replacing the A/C/Heater temperature controls might help, (although this was replaced about 5 years ago).

There don't seem to be any vacuum leaks anywhere, and the intake manifold gasket was replaced about 5 years ago, and isn't leaking again yet.

Even though the truck has 209,000 miles on it, I can't imagine that there's a problem with the fuel pump (i.e., low pressure), coil, or timing chain (i.e., play in chain), because the truck runs perfectly until it's hot.

And since this is a 1991, there's no MAF sensor, Crank/Cam Position sensor, or even an air pump.

I'm running out of ideas.

Start a new thread with a link to this one in the full size forum. That member has not been on the site since June of 04 so i doubt anyone knows if he fixed his issue.