Idle speed
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Senior User
Joined: Jul 2003
Posts: 423
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From: Nova Scotia, Canada
Idle speed
I have an 1988 F-150 with an SEFI 5.0/C6 combo. Right now during a cold start up it revs immediately to 2000rpm and then in 30 seconds or less it falls back to 1000rpm. It idles at 800rpm in gear with the engine hot and I think this is kinda high. I can't see any tags on the truck that say what the idle speed should be and my Haynes manual doesn't say either.
The truck works great and isn't too bad on gas but I'd like to turn the idle down some if possible. Niether the dealer or myself has been able to access any codes or do any diagnositcs with the ECM as the previous owner(s) has messed with the wiring by replacing some relays on the LF inner fender. None of the wire colors match what was originally in the truck. Could there be anything else making the idle speed up?....like a sensor or something?
The truck works great and isn't too bad on gas but I'd like to turn the idle down some if possible. Niether the dealer or myself has been able to access any codes or do any diagnositcs with the ECM as the previous owner(s) has messed with the wiring by replacing some relays on the LF inner fender. None of the wire colors match what was originally in the truck. Could there be anything else making the idle speed up?....like a sensor or something?
Senior User
Joined: Jul 2004
Posts: 484
Likes: 0
From: Roland, Ar
The idle speed is controled buy the ECM, the ECM uses the Throttle Air Bypass valve to control the speed and is not adjustable. Remove the valve and clean it with carb cleaner to see if that helps, also check for vacuum leaks.
