Ive had a hissing sound coming from my engine for a while and havent been able to track it down. Sprayed carb cleaner and didnt find anything. Did a smoke test today with a cigar and found smoke coming from somewhere around the throttle body. Couldnt really pin point a spot. What would be spots where it could leak out? I know the main gasket and also that little elbow for the map sensor. Also, when i open the butterfly and let it go, it slams shut but then it sound like a second flap is closing after it. Kinda like a lid slamming or marble dropped. But after the initial main slap of the butterfly closing. It idles okay, not great but not like its going to die, just a little jumpy. Its a 2000 4.0 aw4. any help would be great!

 

That second sound might be the gas pedal jumping after you let the throttle slam shut..disconnect the throttle cable from linkage and see if it goes away.. Also make sure none of the rubber nipples are cracking and leaky that hook to the TB..

Ive seen the little o-ring around where the IAC is go bad and start to leak. Also the little gasket for the IAC might be bad. I would check there also.

 

ill try that tomorrow. and do all the sensors have a little gasket to them?

 

No just the IAC has that little one and rubber O-ring. The Map has a little rubber elbow that hooks to the TB check that also just to make sure.