I did a search for idle issues but didn't see a headline with something similar. The car starts well enough. Will have a slightly rough idle at start, fluctuating between 600-1200rpm until it warms up above the white line. then it will idle steadier between 900-1100rpm.
however at times, when im running from place to place the idle will go go from 400-1500 as the ICV (idle control valve?) is trying to keep the car running. Sometimes it will stall.
Running on the highway or anything that will keep the revs steady will be fine, but at idle i get all that mess. at times a good throtling will seem to bring it back to its senses. note that i don't get stuttering when pressing the throttle.
some treads at other sites point to the MAF, other to the temp sensors...
(as a newbie to both 928OC & Rennlist, this may be sacrilege BUT...)
FWIW- I'm having issues with my 84- which is a different animal from your 86.5. However, in the process of troubleshooting my Eleonore, I've encountered quite a few issues quite similar to yours on...that other 928 forum. Some old, some new.
Whatever the case, I hope you get yours running better soon!
1) Find the Temp II sensor on the top front of the engine. There are two different sensors in the housing, one for injection, one for ignition.
2) Check the electrical resistance from each pin to engine ground (earth). The resistance at 15-30C should be 1.4 to 3.6 kOhms (note the "k"). The resistance at 80C should be 250 to 390 Ohms.
3) Remove the large connector on the LH ECU. Determine the pin numbers. Check the resistance between pins 3 and 5. With the throttle closed, there should be close to zero Ohms; with the throttle opened a small amount, there should be infinite Ohms (open circuit).
4) Locate the Idle Speed Control connector on the cross-bar at the top front of the engine. There are three pins in the connector. Make a jumper to connect the pins located at one o'clock and six o'clock. This kills the idle speed control. With the engine fully warmed up and the jumper installed, adjust the idle speed to 680-700 RPM. The idle speed adjustment is on the throttle housing, down between the first and second manifold tubes on the right side of the engine (left as you are facing it). Remove the jumper.
