When my car is at idle, my understanding is that intake pressure should read zero on the VAFC and vacuum should read -20. recently i noticed that intake pressure is at .2-.3 at idle and vacuum reads -18. The throttle gauge shows that there is no throttle. Any suggestions why i'm not getting correct readings? btw, no CEL codes.

 

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What rpm is your car idling at? When mine is at 600-700, manifold pressure is around -21 or so. However, my car acts a little strange when it's below freezing outside (a recent development as I just moved from east TX where it never freezes). The motor idles between 1100 and 1500 rpm's in these conditions for some reason, and I have noticed that manifold pressure is about -18.

I never could resolve the problem. Temps warmed up, and now my car behaves normally, but idle was pretty bad there for awhile.

 

well the vac is around there, but a few weeks ago, it was at -20 and 0 intake pressure at 700 rpm idle. car ran perfect and smooth. this was consistant. suddenly it's not. the idle feels a little shakey and seeing numbers off from what i kno to be a norm scares me. if anyone has info, please help.

 

Sounds pretty similar to what I experienced. Even resetting the ECU didn't work. However, after things warmed up a bit, I reset the ECU again and everything was fine. It certainly doesn't sound like an internal problem with the motor. I'd say at worst you may be looking at a problem with your IAC valve. I'm guessing the cold air made mine stick or something. These kinds of problems are such a pain...