82' 911SC Idle Problem

rubenmad · 02-19-2002, 09:21 PM

Ok guys. I've search the archives for all issues concerning a rough idle, and there is alot of information. This is what I'm experiencing:

1. The car dies after the first crank.
2. On the second crank, it idles at at about 1100 RPMs.
3. When warm it drops about 900 and then to about 400.
4. After I drive it for about 15 min and is completely warm, it increases to 900 rpms.

5. In some cases the idle has dropped down to 400 rpm and sometimes dies after it has been running for a while. This I dont understand.

Upon inspecting the WUR, I noticed the the wiring harness was disconnected. I connected it but did not notice an improvement.

The car has had a valve adjustment, cap/rotor/spark plugs have been changed, the CO mixture was adjusted about 6 months ago, and the oil has been changed.

What do you guys think may be the problem? I think it may be the WUR or the AAR.

Thanks in advance,
Ruben

Graham Archer · 02-20-2002, 06:20 AM

The disconnected WUR is not a good sign. Perhaps you should see if it is getting power and the resistance across the terminals is acceptible (sorry I don't have my manual with me so I don't know the correct value)? Ultimately the fuel pressure should be checked during warm up.

It sounds like you are fighting a lean mixture. Have you checked the dwell on the frequency valve when the car is warmed up?

Is the O2 sensor connected? When was it last replaced?

john walker's workshop · 02-20-2002, 07:15 AM

perhaps someone adjusted the mixture with the warmup regulator unplugged. or maybe they did it when the relay for the lambda computer was dead. under the passenger seat is the computer and the relay is at the left front corner of the computer. when the engine is warm, unplug the relay and see if the idle gets rough. that would indicate that it is working. the relay gets power from the domelight fuse. when you have checked for power at the warmup reg and you know the lambda system is working, have the CO set by a shop at 3.5% with the oxy sensor unplugged, and leave it unplugged for smoothest running. at the time, set the idle speed to 950-1000RPM. then see if that does anything for the poor idling.

rubenmad · 02-20-2002, 07:40 AM

Graham, I will check the resistance across the terminals of the WUR. What would be the symtoms of a disconnected WUR?? I didn't check if the O2 sensor was connected, but it was replaced in July. My car was running rich and did not pass the smog check. When the mechanic tried to set the CO settings, he couldn't because of a bad O2 sensor. As John mentioned, I hope he didn't adjust the CO mixture with the WUR disconnected!

I was thinking it may be the AAR because of the low idle during cold start up. Any more ideas?

Thanks
Ruben

wckrause · wckrause's Garage

Having the WUR disconnected will only effect how long it takes to warm up and start generating the correct mixture. If it doesn't get power, then it will just take longer for it to heat up via the engine heat.

Graham Archer · 02-20-2002, 09:39 AM

You can test the AAR by removing it and looking through the bore. It should be just about closed at room temp. and fully open after you put it in the freezer for a while. However, I doubt the Bay Area temps are low enough to cause it to open all that much. I would still suspect a lean mixture. Vacuum leaks are a typical culprit in my minimal experience.