91 Metro still rough idle

I have pretty much done a complete tuneup on my car ( new plugs, wires, distributor cap, rotor (soon), PCV valve. Cleaned EGR valve, fuel treatment, lots of carb cleaner, fuel filter (soon, its being difficult).

Runs better than ever, Great mileage, at speed.

Still can idle rough to VERY rough :^(. Rarely, VERY smooth :^), but sometimes.

I've read some archives here and have had a few ideas leading to the electrical system then tonight I discovered something new.

The car runs pretty good during the day most of the time. At night after work it can be tough to get it to idle smooth when I first start it. Tonight when I got near home I stopped for a burger. Sitting in the drive through line I noticed when I let my foot off the brake the car would run pretty smooth :^), foot back on brake was a rough idle. Then the light bulb came on over my head, Doh.I had the headlights on ( bright only work) and the radio. Brake lights or whatever seemed to put it over the edge to a Very rough idle.

Where do I start with the electrical system ? Battery, alternator, coil ???

Or what ? I'm starting to think its not a burnt valve or piston and this car might last a while longer. Haven't wanted to pay for compression test or computer analisys, Last resort.

Thanks, John

Sounds like your engine is starting to show it's age. They tend to lose low end torque when they get old, because compression in the cylinders is no longer even, and you get blow-by on the rings. Turning your idle up 100-200RPM's should remedy the problem for now.

I guess I'm just expecting too much, I'll try and kick the idle up a bit.

Thanks, John

Well, I could tell you to drop the oil pan, pull the head, take the pistons out, hone it, and re-ring it. But upping the idle just seems like a far more efficient idea :smokin:

I just thought I read somewhere in the archives a weak electrical system might cause some ignition problems at low RPM. Guess not.

Thanks again, John

Well, you've done a complete tune-up on it. Ony other thing you could really do to improve the spark is to put an MSD coil in. It would have minimal improvements in the low end. It would stop mis-fires and engine missing.

I have the same rough idle situation with our '92 Geo Metro XFI. Just replaced the resonator - that part of the exhaust system about midway between exhaust manifold and rear muffler - hadn't noticed the roughness of the engine so much before that fix... you noticed the noise more than anything else! :)

But after replacing the resonator - the rough engine at idle was more noticeable. Cleaned spark plugs, set gap to 0.039" per info on inside of hood. Set timing to 5 BTDC per same information, after shorting test contacts as instructed. Still rough. Cleaned throttle body and replaced air filter. Still rough. Increased idle slightly - still rough, though not as much.

I haven't checked compression, yet, so I'll do that to see if it's a compression issue. I know it's probably in the archives, but what's an acceptable compression - 140?

Alan, you mentioned that lower compression in one cylinder may cause a rough idle as engines get older. There's about 180,000 miles on our XFI with no engine work, yet. I wonder if adding STP oil treatment or something like that would increase the compression and smooth out the idle. Anyone tried that?

with 180,000 miles, no oil treatment will really help out compression. That's a ton of miles on the 3 banger. Most of em' don't last past 125k without needing a head or rings. You can pick up a rebuilt shortblock on Ebay for about as much as all the machining work, bearings, and new rings would cost, and it would be a lot less work. If I'm not mistaken, stock compression on a 3cyl should be around 185psi from the factory. Anything under 140psi would mean your engine is on it's way out. If one cylinder is 10psi lower than any other, that could be almost considered a dead cylinder. It's being dragged along for the ride, and putting out just enough power to turn the crank for the next piston to do it's thing.

Have you tried a timing belt? It could be strechy and about to give it up. That might wreck your whole day.
I would definately shy away from anything but 5W30 oil. The rings in these like to get stuck in a compressed position and then they just pump oil up into the compression chamber and foul the plugs as fast as you can put them in. This can happen on one cyl and give you trouble idle fits. I have re ringed and honed mine. Had the head redone too. It was the easiest motor to work on I've ever seen.
Even tho,,I like the option of a new or low mile motor swap.

Stretched timing belt... That sounds interesting.

Would a stretched belt cause rough running at idle, but not effect engine at higher rpms?

On our XFI with 180,000 miles, I don't think the timing belt has ever been changed. I just checked the log I've kept on the car, and I see the fuel filter hasn't been changed, either.

Anyone know how often the timing belt should be changed on these 3 bangers?

How often should the fuel filter be changed? Thanks, Rick

Well that might be a long shot but it definately needs to be changed. I'm going to change mine very soon but because I'll be under the timing cover to change crank and cam seals cause they're leaking and I don't want to go through the same steps again.
Hey here's something easy to try. There are a couple of ground wires from the engine to the firewall up high near the center. Try re-establishing a good connection with these and also the screws that hold the coil to the firewall. And any other electrical device that is mounted to the firewall.
Also one of the ground wires has a connector about halfway. make sure it's tight.
I'm guessing your geo should be on it's fourth timing belt.
My '93 has a fuel filter that is crammed up near the driver side front corner of the tank. Seems like I had to pull some brake line aside and get lots of dirt in my eyes.
Are you in Oregon? I'm in the west Portland area.

i would suggest checking for a vacuum leak for the brake/idle rough thing. maybe for the whole system you might want to replace all the vacuum lines

Hey gungadin, yes I'm in Oregon - over on the east side near Burns. Vehicles last a long time over here, because of the dry climate I think... or maybe it's because I hate to let them go... 8) I agree with you on the fuel filter... I changed one on our 93 Metro a few months ago - was really plugged up - and was pretty tough to get to.

I should probably do some engine work on the 92 XFI... I notice there's a little seepage of oil near the number 1 cylinder, so I probably need to replace the valve cover gasket or maybe the cam seal on that side. And while I'm at it, I should change the timing belt, too. Just need to find time, as I've got other rigs and projects to work on. And, aside from a slightly rough idle, the XFI runs great at cruise speed and still gets around 60 mpg. Has paid for itself at least 3 times in fuel savings since we bought it new. Well, I'm out the door to continuing drilling a well. Thanks for your insights -- and thanks for the feedback from others, as well. I appreciate winnetcom posting this thread, too -- got a lot of useful information from several knowledgable people. Later, Rick

This is an excellent suggestion. Also the intake manifold or carb could be loose and give you a vaccuum leak. I use the dangerous method of squirting starting fluid (highly combustable and no darn good to breath) at the mounting surfaces of the intake and vaccuum hoses while the car is running. When you get to the leak the motor will idle up. Best to do this outside in a breezy place to keep the vapors cleared out. Or sometimes you can zero in on a vaccuum problem by just pulling a hose in a direction that might close the leak or pushing or pulling the carb/intake.

Rick,
I believe the reccommended timing belt replacement interval is every 80k miles

Hey Rick I'm in the water biz too. Good luck today,
I think winnetcom has the best idea.
I rescued and rebuilt my '93 metro from the blackberries down on the coast in Port Orford. It's the most faithful car I've ever had. Man what a money saver eh? I've got 55K on my re ring hone head and rod bearings.
The oil is very clean and clear.
My machinest told me that the lighter 5W30 is necessary for the valve train. He says the heavier oil doesn't allow the valves to fully close and causes them to burn.
Nice weather eh? We're making 60 milliion gallons a day of drinkin' water for the last two days. I tell you these people are THIRSTY!!!

This is the kinda tip I was looking for :^) The strange way my car runs as indicated in the start of this thread may be caused by a bad ground. That could explain alot. Seems the coil is kinda close to the ground from the destributor, sometimes arcs if I pull a plug wire. I have suspected from the start that area could be a problem... I'll check it out thoroughly.


Hey here's something easy to try. There are a couple of ground wires from the engine to the firewall up high near the center. Try re-establishing a good connection with these and also the screws that hold the coil to the firewall. And any other electrical device that is mounted to the firewall.
Also one of the ground wires has a connector about halfway. make sure it's tight.

Okay mine did exacly the same thing. There is an ISC solonoid on mine that increases the idle speed under an electrical load. On mine the solonoid valve and the computer output that controls it were both bad. I replaced the valve and restored it's operation with a relay since that one output on the computer was shorted. Now it works fine, 45mpg and smoothe idle too. I can give more detail if interested. Mine was a canadian model with manual transmission. Not all models have the same idle speed control.

Larry

When you say the output on the computer was shorted, how did you fix that? Did you replace the computer? Or are you talking about inside the ISC? Let me know, thx.

HEY DanMan,
Sorry I’ve been gone awhile. I’ll try to explain.

HOW IT WORKS
The idle speed control (ISC) solenoid is an air valve that lets extra air into the throttle body just as if the throttle were slightly open. On my 91 metro it increases the idle about 110 rpm. It only comes on when a load is present and allows the engine to idle smoothly with a load. The valve is powered up from the fuel pump fuse and has power whenever the fuel pump is on. The ISC valve only comes on however when the computer senses a load. When a load is present the computer grounds the solenoid valve so it comes on. The way the computer senses a load is unique. There is a block of several diodes in the wire harness near the inside fuse block. Several circuits are wired to the diodes so that if any one circuit is on, power comes out of the diode block to the computer. When it works right, the computer gets about 12 volts at the sense terminal when the headlights, brakelights, radiator fan, or heater blower get turned on, then the computer grounds the solenoid to increase the idle speed.

WHAT I DID
When I replaced my ISC solenoid, the valve was always on and the engine idled too fast with no load. I found that power was present at the computer sense terminal only when an electrical load was present as expected. However the ground connection from the valve to the computer was always grounded. Either the wire was grounded somewhere or the computer output was shorted to ground. Disconnecting the solenoid ground from the computer made the valve go off so the wire was not shorted to ground.

RESTORED ICS FUNCTION WITHOUT COMPUTER
I realized I could restore the ISC function with a simple relay and all I needed was a 12 volt relay and an additional ground wire. The coil of the relay gets the power from the diode block on one side (this was the sense wire to the computer). The coil is grounded on the other side. The relay comes on when a electrical load is present. The normal open relay contacts are hooked to ground on one side. The other contact is hooked to the ISC valve (this was the wire from the ICS output terminal on the computer). Now when a load is present the relay comes on and the valve comes on.

RESULT
It works great. I can’t believe how much better the car drives. Smooth idle at load and at no load. I get about 45mpg. I hope this makes sense.

Larry