Rough Idle issue

[BennSport]

Hey everyone, I’m struggling on a low/stumbling idle on my 83 944. It sounds like there is a hissing sound coming from under my intake manifold, but I can’t entirely locate it. I assume it’s by my auxiliary air regulator but I’m not 100% sure. I pulled the connector to the air regulator while the car was running and nothing changed. The idle becomes rougher the longer the car is running. Any help would be greatly appreciated, thank you in advance!

[Tom]

Sounds like you have a vacuum leak. If you can hear it, you might have luck pinpointing it with a cheap mechanics stethoscope, or even a close visual inspection. If not, doing a smoke test is almost a rite of passage on the 944.

https://www.amazon.com/AutoLine-Pro-Aut ... 9hdGY&th=1

https://www.amazon.com/Mechanics-Stetho ... 7818&psc=1

[BennSport]

I tried using a mechanics stethoscope to no avail unfortunately, I’m afraid I might have to bite the bullet for a smoke machine. If it is a vacuum leak by the air regulator would that cause the idle to get progressively worse as the car keeps running? On initial startup it’s running at around 600 rpm

[Tom]

I tried using a mechanics stethoscope to no avail unfortunately, I’m afraid I might have to bite the bullet for a smoke machine. If it is a vacuum leak by the air regulator would that cause the idle to get progressively worse as the car keeps running? On initial startup it’s running at around 600 rpm

Yes. Any vacuum leak will make the car run leaner than intended. When the car is cold and warming up, it's programmed to run richer than normal, since the fuel does not atomize as well until everything is fully up to temperature. So it is very possible the extra gas when cold is helping to offset the extra air from the vacuum leak, and as the car warms up and leans out your car might be getting leaner and leaner -- and running worse and worse...

[gb951]

I built my own smoke tester for about $15 after watching this video...

[BennSport]

I ended up spraying some starter fluid around the auxiliary air regulator and the rpms picked back up. Now it’s just a matter of removing the intake to find the leak. Hopefully it’s just the hose and not the regulator itself!

[Tom]

I ended up spraying some starter fluid around the auxiliary air regulator and the rpms picked back up. Now it’s just a matter of removing the intake to find the leak. Hopefully it’s just the hose and not the regulator itself!

Good work. Once you get the intake off, I'm guessing it will be pretty obvious...

[BennSport]

Hopefully, I’m just glad I didn’t need to go out and purchase/build a smoke machine. Are the intake gaskets 1 time use? Or can I get away with reusing the same one if it’s in good condition?

[Tom]

Knock on wood that's the only leak.

Intake gaskets are one time use, and I've gotten away with reusing them if they still look good.

[dme]

Knock on wood that's the only leak.

Intake gaskets are one time use, and I've gotten away with reusing them if they still look good.

Ditto. As often as you remove the intake to get to (or make easy to get to) other things, I'd go through intake gaskets like the proverbial waste through a goose.