Dan Dragner

Hi, everyone. Still trying to pin down a bad misfire...I think it has something to do with a whistling sound (read vacuum leak). The sound is definetly comming from the center/ top part of the engine....about the throtle housing. I have disconnected the brake, and climate lines, also checked for any bearing noises. All OK. The noise is gone with the throttle in the idle position, but openning the throttle even a tiny bit (100 rpm's) starts this whistle. It is most definetly a vacuum/air type noise. What should a '86 with 140,000 miles pull at idle for a vacuum reading ? Mine is pulling 23ish, but the reading drifts. What should it read at 2500 rpm's....?
I have performed the Porsche Tecnik intake test (pressurizing the intake system to 25 psi, listening for intake leaks) AND FIND NONE ! But what about this whistle ? Are leaky valve cover gaskets a good guess ...?
Thanks, Dan

Randy V

Based on your description, I'm betting it is either a loose seal between the intake plenum and the engine (most likely, will also cause poor performance due to vacuum leak), or improper seating of the lower airbox seal.

If your valve covers (cam towers) were leaking, you would see oil leaks.

Incendier

I'd agree with Randy's assessment - there are two o-rings that are suspect. BTDT.

The first sits in the throttle body throat and seals the airbox intake to the throttle body, the second is between the throttle body and the intake proper.

Mine leaked, light whistle but big down on performance. They get flat edges over time.

P/Ns are 999 701 436 40 and 999 701 599 40 for the l-jet and 999 075 341 02 and 999 701 183 50 for the lh-jet.

Good luck.