ltoolio

Hey all,
Been a while since I posted a "help" thread, which is a good thing.

OK...a bit of background.
- Car was on lift bars for close to a year. No real mileage put on it during that time.
- Did a whole lot of clean-up on the car...grounds, electrical connections, Deoxit/Stabilant everywhere, hoses.
- Before car went up on the bars, I had some pretty serious idle issues. Would die at stop lights. This isn't that bad, but it's still not ideal.
- PO replaced the Temp II right before I bought the car.
- Since getting her of the liftbars, I've probably driven her ~400 miles (which, incidentally are the best 400 miles I've ever driven in a car).
- My AFR gauge seems to run in the "normal" range, per here.
- I've gone through a tank and a half of gas, from different stations, with the same symptoms. I've also popped in the Techron FI Cleaner Roger suggests.

Symptoms:
- At cold start (which happens right away...didn't happen before all the clean-up), car idles pretty steadily around ~750, although there are brief moments of rough idle that she quickly recovers from.
- After the car warms up, she drops to somewhere near 300-500 on idle. Idle gets rough, but car hasn't died (yet). Feathering the throttle brings her back for a moment, but then slides back down to the low range.

I've read a number of threads here on the topic of rough idle, and have seen a number of suggestions of the problem - LH, EZK, Relays, Temp II, O2 Sensor, vacuum.

I figured I would try swapping out the 53B relays tomorrow to see if there's any difference, but if not - is there a suggested plan of attack/testing given how she's behaving?

Thanks, as always!

GregBBRD

Since the car starts and runs, you can forget the relays....that's not the problem. Also probably not the LH or the EZK.

Check/monitor the output from the O2 sensor with it hooked up and report back..

(It should be right around .5 volts when cold. After a couple of minutes, it should slowly increase to about .8 volts and then begin to fluctuate between .2 to .8 volts every few seconds.)

The Forgotten On

In my 81 the idle screw (large screw right in the front of the throttle body) was set too low and kept the idle around 400 and was very rough unless I feathered the throttle.

I unscrewed it to raise the idle and now it sits comfortably at 650. An early 928 should go up to around 1000 rpm when started cold and drop down to 650 when warmed.

I would recommend raising your idle first in your 82 as everything else seems to be fine. Also, check to see if you have excessive carbon buildup in your distributor cap which could cause a bad spark.

ltoolio

Thank you gentlemen. A question about the following:

Am I disconnecting the O2 Sensor from the green connector, then using my multimeter to test against the leads coming from the sensor itself?

I shall do that as well. Thinking of order, I'll go:
- O2 check
- Distributor cap check
- Idle screw

Figured I'd get diagnostic stuff first, then adjust idle once I know (or fix) the mechanics/electronics are good.

The Deputy

This is what cured my 84 of its fluctuations while idling, after warm-up. You could hear a vacuum draw around the screw itself, twistered the screw in and out a couple times and readjusted until it smoothed out and then set the idle where I wanted...and all was good. Vacuum leak sound disappeared, too.

Brian.