I have a 1990 F-150, fuel injected 5.8 (351) engine. It normally idled at about 700 RPM, according to the tach. I guess the computer compensated for the air conditioner in warm weather because the idle was the same summer or winter.
Recently, the engine just refuses to idle. I can start it (starts easy), drive two miles and stop, and the engine will die. About the only way I can get it out of the driveway or keep it running at low speed is by keeping the accelerator pushed down a little. I cannot find any adjustment for the idle. Any ideas?
The idle is controlled by a little valve called the IAC (idle air controller) or IAC valve (idle air control) valve. If you disconnect the wires that lead to it, does the car do the exact same thing? When you first start the car, does it rev higher and then lower to 700 or is it always at 700? If the latter, then the computer may simply need to be reset because it seems that the IAC is adjusting.
To do this, disconnect the battery for about 20 minutes. Then start the engine and do nothing for about 10 minutes. If that doesn't help, then the ports may be carbon blocked and need to be cleaned. The IAC should remove with two bolts from the side of the throttle housing. Get some good fuel injection cleaner and spray away! You may need to replace the gasket, so you might want to pick that up first. Then, if this fails, you may have to replace the IAC itself.
Bob, The Auto Answer Man
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