1991 sunbird idle

[juice410]

My 1991 Pontiac Sunbird idles very high randomly. At times it idles fine and then suddenly the idle goes up high. I have replaced nearly every sensor and still can not fix this problem. I was told that perhaps the computer has gone bad. Has anyone had this idle problem before. How does one test the computer to see that it is bad. I do not want to spend $100 for a computer just to find out this is not the problem. Any suggestion will be greatly appreciated.

Thanks juice410

 

[melsg5]

if your vehicles is equipped with an idle air control valve, have you tried cleaning or replacing it? have you cleaned the throttle body?

 

[92 Sunbird LE]

Could also be a bad TPS or the EGR is clogged / leaking or its gasket is bad or you have vacumn leaks.

No codes?

Doug in P.R.

 

[Lokim]

The next time it starts idling high, first check the connections at the ECM. Make sure they're fully seated and tight.

If the connectors check out, and if it has a removable PROM, you may want to check that it is still fully seated. If that's OK, use the handle-end of a screwdriver to firmly (but not HARD) tap the computer case in numerous places on every side at all angles. I've diagnosed more than one bad ECM that way.

What you're looking for is any change in the engine's behavior. If it goes back to a normal idle or coughs, sputters, hiccups, dies, whatever, you likely have a bad ECM.

You can also try the "tap test" when the car isn't idling high to see if you can induce the symptom.

Again, if the tapping/wiggling produces a change, it's probably time for a new computer.

______________________________

 

[Lokim]

I would also check the battery connections. Clean the living hell out of the battery terminals AND the contacts on the battery cables.

I usually start by chipping/scraping the corrosion off with a flathead screwdriver, then finish up with a pneumatic die grinder with a wire wheel or scotch-brite disc. If the die grinder isn't available, a stiff wire brush will suffice. Just make sure the contacts are CLEAN and the ground cable is connected clean and tightly to the engine AND the body.

I can't even begin to tell you how many weird little electrical gremlins I've solved by simply starting my diagnostic procedure with a hardcore battery service!

I guess it's a good thing that my high school auto shop teacher drilled the following into all of our heads -

"ALL ELECTRICAL TESTS START AT THE BATTERY!!!"
-Mr. Eddy

Good luck, and keep us posted!