What causes the idle control valve to rev up the engine?

[rcslineman]

My '96 f150 302 revs up all the time (2k) and I cannot afford wasting this high dollar gas. Unplug the ICV and it idles fine. Looking like it may be the MAF sensor, but not sure. Gimme me somethin smart guys.

[Conanski]

If in fact the IAC is opening and allowing the motor to rev high, it's because the computer is getting faulty info from it's sensors and it can't control the motor. You would have some codes stored if this is the case. If you don't have codes stored you probably have a large air leak past a gasket or through a vacuum line.

[IcemanV8]

That's exactly what my 86 does, and codes show out of range TPS. Except mine idles high with the plugged in (1500RPM sometimes, and sometimes 2000RPM), but if I unplug the TPS, I idle lower at the cost of running way too rich (fuel in oil)/loss of power/unresponsiveness. I just leave it in most of the time to avoid fuel in oil.

Check your idle screw, too. If you unplug the IAC and it runs FINE, it sounds like the idle is set too high. It supposed to barely idle (500RPM or so) with it unplugged, so try adjusting that, first.

[rcslineman]

Finally fixed it, the TPS was my entire problem. Thanks for the lead Iceman.

[IcemanV8]

Thanks for the update. I can update saying I fixed mine a few weeks ago, also, and it was the TPS. Nice being able to idle again, isn't it? That 2k RPM stuff was killing my mpg.