83’ 944 engine surging

[Magic944]

I previously posted about this issue but I can no longer find the thread. My 944 has had a surging problem at idle/low speeds and I diagnosed it to be the auxiliary air valve by clamping the hose leading into it. After changing out the auxiliary air valve for a new one I’m still getting the same issue. Is it possible it’s the electrical connection?

[Matt at Pelican Parts]

Hi Magic944,

It looks like the post you're looking for can be found here:
https://forums.pelicanparts.com/porsche-924-944-968-technical-forum/1154397-1983-944-surging-idle.html

Have you checked/cleaned the Idle Control Valve? It can also cause that symptom if it becomes gummed up

[Magic944]

Thank you, if I don’t get a response I’ll add it to that one. The ICV is only equipped on later cars. Because my car is an early car it has the auxiliary air valve instead

[Monkey Wrench]

did you do the smoke test? hoses that handle crank case fumes may be pretty decomposed at 35 years. if any air can get in by some "back door" that isn't measured by the "barn door" will upset the air fuel mixture. I also understand its not easy to see in the area, I wondered if rad removal may help . or if the intake needs to be removed for better access.

on clarks garge there is a bit on cleaning the device that monitors airflow, ( AFM) evidently there is a copper trace and a wiper and cleaning that may help because tarnished contacts may produce inaccurate results and maybe cause rough running or jerky acceleration. It mentions how to reposition the wiper so it uses a fresh spot..

basically as the barn door opens it moves a potentiometer, and when that gets dirty it's a bit like a "scratchy volume control" on a radio.. and then the ECU doesn't like the bad or "scratchy" signal. that would in turn cause bad signals to the injector with the wrong dwell ( injector open time) resulting in too much or too little fuel or erratic behavior. That sounded similar to the issues you report.

https://www.clarks-garage.com/shop-manual/ts-01.htm#idle-surge

and

https://www.clarks-garage.com/shop-manual/elect-22.htm

id be careful with the AFM, if you go mucking about with it you may upset its calibration, but maybe its possible just to clean the wiper track? if you have a spare maybe it can be swapped to note differences.

[Jfrahm]

As above. Cracks in the J-boot or ISV hoses, etc. is a common cause of surging.