944 Progressively Worse Idle

[massive]

Noticed a strange new issue with my 944 today. (1984 Square dash 8V)

Did a run a lunchtime (probably about an hour or so) all appeared normal until near the very end of the journey where the idle of the car appeared to get progressively weaker.

Then, did another run late afternoon (this time only around 30 mins of driving total) and same thing.

Both times car started ok and idled fine, but got weaker towards the end.

Anyone got any pointers to start checking, temperatures and oil pressures seem normal and battery is not that old and shows good voltage. Car was serviced in December 2020.

[John_AZ]

Hi Massive,

944 Progressively Worse Idle...(weaker)

My worse idle was rotted hose to the "Y" connector- PART 7

Check hose connections under the intake. Tighten hose clamps. Check for rotted hose.

I do not think it is the ICV-idle control valve, throttle valve or MAF, but all are possible.

Next (IF NECESSARY)----remove the intake, new seals and more hoses to check



Go to Porsche Classic parts catalog for more pictures:
https://www.porsche.com/usa/accessoriesandservices/classic/genuineparts/originalpartscatalogue/

Just a few possibilities. GL

John

[massive]

Originally Posted by John_AZ

Hi Massive,

944 Progressively Worse Idle...(weaker)

My worse idle was rotted hose to the "Y" connector- PART 7

Check hose connections under the intake. Tighten hose clamps. Check for rotted hose.

I do not think it is the ICV-idle control valve, throttle valve or MAF, but all are possible.

Next (IF NECESSARY)----remove the intake, new seals and more hoses to check



Go to Porsche Classic parts catalog for more pictures:
https://www.porsche.com/usa/accessoriesandservices/classic/genuineparts/originalpartscatalogue/

Just a few possibilities. GL

John

Thanks John, I will give those a check.

I did replace the Y connector and vac lines for some new ones a couple of years ago, but will give them another look.

[Jfrahm]

Could also be fuel leaking into the vacuum system. Let it idle badly and then check the plugs. Also check for fuel in the vacuum lines for the FPR/Damper.

"loading up" from excess fuel will cause the idle to deteriorate.

[John_AZ]

more...
The MAF has been mentioned as a source of numerous problems.
This should be the last item checked or modified.
There is a procedure for changing the wiper arm contact inside. Do not change the position immediately---just clean the base and the contact. The top has to be resealed with special glue.

Do not change the MAF adjustment screw (hidden under the metal plug on top). I did-only after I bottomed the screw and counted the rotations down to 1/8th ( mine was 4.5 rotations to bottom)

A good easy repair is the TB throttle body reseal.

John

[walfreyydo]

1-a bad DME temp sensor could also be the culprit, not letting the DME know the car is warmed up thereby creating a richer mixture and causing issues only once car is warmed up. Can be easily tested.
2-As mentioned, vacuum leaks can also cause surging/rough idle conditions. Harder to pinpoint but possible with compressed air.
3-ICV's commonly get gunked up over time, so this is worth checking, and cleaning if needed. (requires alot of work removing intake manifold, which is why its #3)
4-AFM worth checking if all else fails, but logically doesnt make sense why AFM would be a problem only when engine is warmed up.

PS: Our cars do not have a MAF (or MAP), which is a completely different type of air metering system than the AFM (barndoor) system our cars have. (Unless youve done a MAF or MAP conversion of course)

Troubleshooting - Engine