Uneven Idle

1990 Geo Metro, 3 cyc, auto, air, - 81,000 miles - original owner

This car has been out of service, sitting on the driveway strip, for quite some time now. Recently, I decided to start using it again. Because of rough idling, I replaced the the plugs, gap .039, distributor and rotor. About 4 years ago (and very little milage since then) I replaced the timing belt. At that time I did not check the timing. The car ran well enough.

Since adjusting the timing, the car runs fine except for fast stops, say coming down from 50-55 miles an hour, using brakes. It starts to miss but clears up after picking up spead again. A slow or natural stop doesn't porduce this problem.

I did jump the DC at the fuse box and did cover the vacuum advance hoses with tape.

I did check and clean the pvc valve.

I am not a machanic but does this problem sound like the vacuum advance? If so, other that the vacuum from the hoses how does it work internally? Are there any parts to it that can be cleaned or adjusted?

Thanks for any help.

run some in tank fuel injector/carb cleaner. get a nylon brush and some sea foam or aerosol carb cleaner and scrub your carb real good, especially around the butterfly valve - open the butterfly with your hand and scrub all the crap around where the butterfly seats - get it nice and clean and see if it helps. deposits from the pcv system will hinder idle quality on all cars inevitably. after that I would check for a small vacuum leak somewhere, and after that I would start poking around at things like the vacuum advance. I think either the haynes or chiltons gives instruction for inspecting the vacuum advance. goodluck.

mechanicmatt

run some in tank fuel injector/carb cleaner. get a nylon brush and some sea foam or aerosol carb cleaner and scrub your carb real good, especially around the butterfly valve - open the butterfly with your hand and scrub all the crap around where the butterfly seats - get it nice and clean and see if it helps. deposits from the pcv system will hinder idle quality on all cars inevitably. after that I would check for a small vacuum leak somewhere, and after that I would start poking around at things like the vacuum advance. I think either the haynes or chiltons gives instruction for inspecting the vacuum advance. goodluck.

mechanicmatt
Thank you for the advice. I did get injector carb cleaner today and cleaned the fuel injector. I had put fuel injector addative in the gas tank earlier.

Something strange happened today. Yesterday the car was running fine. Took it out and had it up to 55 mph. Spent about 45 minutes driving and putting the car through its paces. This morning, started the car and could barely make it down the street and back, it was missing so badly. Later today I rechecked the timing and it was way off from what it was set to a few days back at 6 Degrees before TDC. After retiming the car today, had my wife rev it up a bit and checked to see if the vacuum advance was working. It was.

On the infor. under the hood of the car, calls for 6 degrees with the hoses to the vacuum advance blocked.

In the Chiltons manual, it calls for a jumper across the computer module under the dash. If I remember correctly, the vacuum advance is controlled by the computer module so if the hoses to the vacuum advance are blocked it is unneccessary to jumper the computer module.

As I mentioned earlier, I replaced the timeing belt sometime back. I had no instructions to go by, so I unloosened the tensioning pulley and took the old belt off, and installed the new one. In installing the new timing belt, I placed it on correctly and let the tensioning pulley put pressure on the belt. I then tightened the bolt that held the pulley. Since the old belt didn't break that was all there was to it. Was there anything else I should have done?

I did clean the ERG valve and the pvc valve.

Thank you for the advice. I did get injector carb cleaner today and cleaned the fuel injector. I had put fuel injector addative in the gas tank earlier.

Something strange happened today. Yesterday the car was running fine. Took it out and had it up to 55 mph. Spent about 45 minutes driving and putting the car through its paces. This morning, started the car and could barely make it down the street and back, it was missing so badly. Later today I rechecked the timing and it was way off from what it was set to a few days back at 6 Degrees before TDC. After retiming the car today, had my wife rev it up a bit and checked to see if the vacuum advance was working. It was.

On the infor. under the hood of the car, calls for 6 degrees with the hoses to the vacuum advance blocked.

In the Chiltons manual, it calls for a jumper across the computer module under the dash. If I remember correctly, the vacuum advance is controlled by the computer module so if the hoses to the vacuum advance are blocked it is unneccessary to jumper the computer module.

As I mentioned earlier, I replaced the timeing belt sometime back. I had no instructions to go by, so I unloosened the tensioning pulley and took the old belt off, and installed the new one. In installing the new timing belt, I placed it on correctly and let the tensioning pulley put pressure on the belt. I then tightened the bolt that held the pulley. Since the old belt didn't break that was all there was to it. Was there anything else I should have done?

I did clean the ERG valve and the pvc valve.

Sounds like you performed a routine timing belt replacement. But you didn't say anything about aligning the timing marks. It is not uncommon for the cam to move when the belt is removed, so it's always a good idea to double check the timing marks at the cam and crank to be sure. 2 of my 21 metros in the last two weeks have sheered their crank/timing pulley keys. The warning signs were unsettable ignition timing, poor performance, and ignition timing that seemed to change itself until finally the crank spun too many degrees inside the timing gear to maintain runable timing - disabling the car. Take your a/c and/or water pump belts off and grip the crank pulley about the belt surface, rotate it with your hands, and check to see that the cam is turning with the crank without play through the oil fill hole. If you've got play, you've got a big problem, if you don't then keep looking. Just a thought. Goodluck.

mechanicmatt

Sounds like you performed a routine timing belt replacement. But you didn't say anything about aligning the timing marks. It is not uncommon for the cam to move when the belt is removed, so it's always a good idea to double check the timing marks at the cam and crank to be sure. 2 of my 21 metros in the last two weeks have sheered their crank/timing pulley keys. The warning signs were unsettable ignition timing, poor performance, and ignition timing that seemed to change itself until finally the crank spun too many degrees inside the timing gear to maintain runable timing - disabling the car. Take your a/c and/or water pump belts off and grip the crank pulley about the belt surface, rotate it with your hands, and check to see that the cam is turning with the crank without play through the oil fill hole. If you've got play, you've got a big problem, if you don't then keep looking. Just a thought. Goodluck.

mechanicmatt
The car runs like a Top now! I reset the timing yesterday again. I think my problem all along has been me and not so much the car. Thank God it is forgiving (to an extent). I found out last yestereday, that after adjusting the timing, I forgot to remove the tape from the vacuum advance hoses and reattaching them to the vacuum advance. Another problem that I created was not making sure the air cleaner container, that sits on top of the fuel injector, was positioned correctly. There is a mating gasket that came off of the container, Half on and half off. And then there were a couple of hoses that attached to the container that, at least one, wasn't installed back as it should have been.

Still and all, the car runs beautifully now. Thank you again for your help.