[Guest]

Last night my car developed that fun fuel cut off idle cavitation described elsewhere. The one where it revs to 1800 or so rpm, drops to 1200, rinse and repeat.

At the same time, the brake, rear light, and battery warning lights came on, and the voltmeter dropped from 14 to 12 to 8 then 6 volts on the way home.

Once in the garage, I pulled the positive battery lead with the car running and it died, confirming that the system isn't charging. I'm okay with the alternator and/or voltage regulator needing replacement. What I'm wondering is, is it possible the low/nonexistent charge is making the TPS screwy, as regards the idle? I really don't have the wherewithal, in both equipment and knowledge to fix the TPS, and wouldn't be real happy if it needs replacement or whatever.

Anyone able to shed light on this?

Oh yeah, car is '87 NA, mechanically stock.

 

[hawkeye]

First of all... never pull any battery terminals while the car is running... ever. I posted a big writeup on this a little while ago.

I would think the alternator is your main problem, if there is no power of course idle will be screwy. Fix the alt first, then work from there.

 

[Guest]

Your alternator may be the main problem, but...It sounds like the typical ISC valve malfunction. It is on the intake manifold surge tank. When you turn the car off, it should make a clicking noise. If it doesn't, something is wrong. Restart and unplug it while the car is runnng. If it runs the same, ie keeps oscillating, then shut off the car, leaving the IAC unplugged. Let it sit for 15 seconds and restart. If it still does it, its your ISC valve. Clean the connector and plug, and plug it in again while the car is off. Restart to see if it was a bad connection. If the car still revs up and down, its the ISC valve. In case you are wondering, the ISC valve controls the idle. ISC = Idle Speed Control. There is a procedure for testing it in the TSRM, but it invlolves removing it and its a pain in the ass. If it doesn't make any noise when you turn off the car and the idle doesn't change when you unplug it, it is almost guaranteed to be an ISC problem. Now you need to take it off and either clean it and rebuild it or replace it.