I always thought that a vacuum leak caused a poor idle to the point of not holding at all. Right? Right.
So answer me this. My car idles horrible and low BUT, if I unplug one of the smaller vacuum ports on the UIM the idle smooths out and goes up.

Hmmmmm?! Who's got an answer?


Thanks

 

Wow, you've got me stumped.

 

you could be running too rich, causing a poor idle. introducing a vacuum leak into the system will make the engine run leaner.
you have an SAFC? try leaning it out at idle and see if that makes it smoother.
other than that, something could be out of adjustment. check the TPS and your timing. and make sure your all your vacuum lines are proper.

 

I have no previous experience with that situation, but my initial reaction is that the AFM might be reporting more airflow than is actually coming through it, and that the new path is at least partially compensating. I might check the AFM, especially since it sounds like your idle isn't stable to begin with!

 

Bingo.
Inducing an intake vacuum leak causes:
1) The AFM to close slightly, causing the AFM to send a lower voltage signal to the ECU, which causes it to think you need less fuel, and
2) The additional air from the intake leak, which the AFM has no idea is going into the engine now.


-Ted