Footballtys3

I bought a 94 mustang base model and it idled high and it would bounce are on the rpms. from 11 to 15 rpms. I unplugged the iac and it dropped the rpms and ran a ton better. Will it hurt my car to leave it unplugged? Will a new one help it?

imp

If it runs better with the IAC unplugged, there likely is a vacuum leak somewhere allowing air to enter unmeasured, confusing the computer. Check all places, hoses for cracks, where air could be being sucked in.

1slow67

It's possible your IAC is also bad.

imp

I believe if the IAC is "bad", that is, not opening at all, AND there are absolutely no vacuum leaks anywhere, the engine will try to fire, but not run, with the IAC unplugged. Thus, I'm guessing IAC OK, vacuum leaks yes.

Footballtys3

So i bought a new iac valve put it in and it ran like it was running with it unplugged

imp

If you want it to run really better, start looking for vacuum leaks. Easy enough to figure out where vacuum is present: hoses, hose ends especially, bad PCV valve, harder to spot intake manifold gasket leaks, worst scenario might be leaking power brake diaphragm.