Irregular idle, thinking it might be temp sensor related...
 

Ok guys. I'm still getting an irregular idle from my car. It just revs up and down between 1200RPM and 1800RPM.

First I thought it was the Idle positioner. Cleaned it out, regreesed it, tested it with a multimeter, and it fully checks out as good. I then checked all the hoses and injectors, no vacuum leaks to be found.

Since the idle positioner is regulated by the engine tempature, I went ahead and tested it with the mutimeter, and I got nothing from the unit. So I went ahead and disconnected the unit and started the car. The idle went to 950RPM but it was really ruff. But at least the fluctuating revs were gone.

Any input guys? Thanks!

-Tony

Sounds like you answered your own question....
The engine temp sensor runs about $25 and is easy to change.
I am having a hot idle surge with my 83 that is going on another post, the research has given me a thought on yours though.

Sooo

You have 87 dme and harness...Is the dme searching for the later models idle stabilization valve?
83 = no i.s. valve
87 = i.s. valve
Seems there should be a fix for this.

The idle bypss valve on the 84 is not regulated by engine temperture. It has a 12 volt heater element in it that is powered by the same circuit as the fuel pump.

The 85.5's and 944S's throttle bypass valve -- idle regulator -- are controlled by the DME via the speed sensor on the flywheel. There is no direct relation to the engine temp.

Now that said. The DME is controlling the valve. Uses a pulsed voltage to possision it. You need an O-silly-scope to see it.


You may need to look at the throttle switch. Even though this may click as the throttle valve seats it may not be making contact.

The idle setting without the Idle Stabilizer is too high. For a late model the idle RPM is 840 +- 50. You need to jumper pin C and B on the service connector to disable the stabilizer and then set the idle speed.

Also just to clarify, the early cars use a temperature operated Auxiliary Air Regulator during engine warm up, and the late models use the Idle Stabilizer during warm up and normal operation.

BTW: My '84 is running with a DME and AFM from an '86. I kept the original harness, so I'm not using an Idle Stabilizer.

12 volt heating element off of the fuel pump circuit. No relation to engine temperture.