Well this car i checked out has a whistle or "chirp" to it when i'm driving, and the guy said the person before him stripped a thread on the intake manifold, could gas or backpressure be escaping from that stripped, screwless hole? and also i was told that i could be losing vaccum in a cylinder because of it. does any of this sound right? and is it harmfull? (i was told it wasn't) and lastly how do you guy recommend about fixing it? (i was thinking about a helacoil)

 

A Heilicoil would fix that just make sure you drill it straight. I just had to Heilicoil one of my exhaust port bolts because the kid I bought the car from crossthreaded a bolt when installing headers. I would think if its a vacuum problem it would have a crappy idle and maybe braking issues at low rpms.

 

There is no "backpressure" in an intake manifold. Its under vacuum when the engine is running. If you are missing a bolt, and the gasket isn't sealing, you have a large vacuum leak, and it will screw up the cylinder that its leaking into. With one cylinder running lean, the PCM sees the extra oxygen in the exhaust, and richens the entire bank in an attempt to get the A/F ratio back where it belongs. You end up with one cylinder running lean and the other three running rich.

You could trace the source of the "whistle" by spraying carb cleaner on the area you think is leaking. When you hit the leak, the whistle will stop and you may get a puff of smoke out the exhaust.