Starts okay, idle stays at around 1500 when warm. When put into gear and clutch in the idle drops to 500 and bounces quickly to 800. I recalibrated the TPS to 1000 ohms properly and nothing changed. The surging seems electrical and the high idle maybe vacuum? Is there anything important I need to inspect that could be the culprit? Thanks, finn.

 

What year? If S5 use the check connectors and give it a try.

 

Yes 1989 S5, are the check connector the green connector near the battery? I'll look around the forum on how to use them, thank you.

 

I played around with grounding the test connector, there are no engine codes and the idle was not effected at all. Why would the idle change so greatly when the car is put into gear? Still searching.

 

Green 3 pin connector side of engine and I use 2 MM to check.
Ignition on, check after up to normal temp, or when cold, move the fast idle cam.
If both show current, turn adjustment screw clockwise until only one has current.
If neither have current, turn counterclockwise until one has current.