New owner of 89 944T and have been driving the car on and off for about 3 months. Everything works great but my rough idle. I tried to takle the idle job this weekend. This was the first time I popped the hood with the engine on and I heard a constant hissing sound near the air filter area or that big rubber tube maybe 5" in diameter that area for sure. Is this normal?

I have a VDO aftermarket guage with vac and boost where sould the guage read?

Thanks,
Will

 

Take a bottle of carb and choke cleaner and spray around the intake boot and the general area - if the engine revs up, you have a vacuum leak wherever you're spraying. It sort of sounds like there's a vacuum leak somewhere if you have a rough idle.

 

if it's around the area of the "J" tube, may have a crack in the tube. i had issues,with that myself

R

 

Normal- NO!

A vacuum leak will cause this exact problem. If you plan on keeping the car- replace them all.
Cheap and easy fix. Inspect the J boot (Intake tube) carefully- they can crack in the accordion or at the 1/2" pickup tube under the J boot (difficult to see) check carefully for tears and cracks, also the Y tubes joining the smaller vacuum lines throughout the engine bay.


My 5$ says the vacuum line to the brake booster AND/OR the J boot is leaking air.