Off idle
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Off idle
Hey guys. I have seem this a million times, but can't seem to find the answer I need. I have a 91 f-150, 5.0, five speed, and headers. I put a new ignition module, and a IAC in. My problem is, when 5 he iac is plugged in, it wants to idle at 1500 rpm, and it's very racey. Almost like an air or vacuum leak. But when I have it unpluged, it's fine. Idles great, runs amazing. I would like to have it hooked up and working with the cold weather, it's a pain in the morning when I start it. I replaced the PCV, cleaned the throttle body with a new gasket, new tps that I calibrated correctly. I don't think the IAC is bad, but any imputed would be great.
Lead Driver
Joined: Aug 2006
Posts: 5,670
Likes: 12
From: Sand Lake, MI
Has the throttle stop screw been tampered with? If so that will need to be addressed.
If not check the tps at its fully closed position, see what its voltage reading is.
Ford Fuel Injection » Throttle Position Sensor (TPS)
If out of spec, closed throttle can be anywhere between 0.6-1.0 volts, say well above that for example, replace it.
If not check the tps at its fully closed position, see what its voltage reading is.
Ford Fuel Injection » Throttle Position Sensor (TPS)
If out of spec, closed throttle can be anywhere between 0.6-1.0 volts, say well above that for example, replace it.
Lead Driver
Joined: Jul 2007
Posts: 7,868
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From: Rhode Island
The engine should not idle great with the IAC unplugged. It should stall or just barely idle at all (~400 rpm). If it idles warmed up at a nice 800-900 RPM with the IAC unplugged, you either:
A: Have a vacuum leak
B: Throttle is not closing fully/Someone messed with the throttle stop screw
C: IAC is faulty and not fully seating.
A: Have a vacuum leak
B: Throttle is not closing fully/Someone messed with the throttle stop screw
C: IAC is faulty and not fully seating.
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The tps was set at full close at .7 volts, using back probes. I belive the idle screw was messed with. But it still wants to idle way to high. Checked for vacuum leaks and none were found. When the engine is super cold, it won't idle for a minute. But if I father the throttle for about 30 seconds, it will idle fine. Only code present is the egr, but I never hooked the pickup back up when I put the headers on. That's no codes KOEO and KOER.
Lead Driver
Joined: Aug 2006
Posts: 5,670
Likes: 12
From: Sand Lake, MI
Short in the wiring was going to be my next suggestion if the TPS was as it should be.
Wht-lt blu wire shorted to ground for example would be all it'd take and easy enough to test for.
Unplug the IAC then test that wire from its connector for continuity to ground with the key off.
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