1991 Ford F-150 High Idle

Tiny
BETHC
  • MEMBER
  • 1991 FORD F-150
  • V8
  • 4WD
  • AUTOMATIC
  • 140,000 MILES
My 1991 Ford F150 will idle extremely high sometimes and the check engine light will come on. If it's doing this when you turn the engine off it won't start up again. Somtimes I would disconnect one of the battery terminals and would be able to start it up again later. Otherwise it needs to be jumped.
What is causing the idle to be so high and would it affect the batteryr?
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Monday, November 17th, 2008 AT 1:33 PM

4 Replies

Tiny
RASMATAZ
  • MEMBER
Clean out the idle air control valve/motor and also look for false air leakage and see what happens
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Monday, November 17th, 2008 AT 2:40 PM
Tiny
BETHC
  • MEMBER
Thanks -will try that but any reason why this would cause the truck to not start up again? Also why does disconnecting the battery seem to help?
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Monday, November 17th, 2008 AT 3:16 PM
Tiny
RASMATAZ
  • MEMBER
Do you have a check engine light?

You've been disconnecting the battery-doing that the computer loses its memory and has to go thru a relearning process.

Next time it w/n start do below to determine if its fuel or spark problem.

Get a carb cleaner and spray into the carb or the throttle body on an EFI. Did it start and die? If not disconnect a sparkplug wire or 2 and ground it to the engine -have helper crank engine over-do you have a snapping blue spark? If so-you have a fuel related problem, check the fuel pressure to rule out the fuel filter/fuel pump/pressure regulator and listen to the injector/s are they pulsing or hook up a noid light. No snapping blue spark continue to troubleshoot the ignition system-power input to the coil/coil packs, distributor pick-up coil, ignition control module, cam and crank sensors- Note: If it doesn't apply disregard it
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Monday, November 17th, 2008 AT 4:48 PM
Tiny
BETHC
  • MEMBER
The check engine light goes on and off periodically. The truck was running good for awhile and the light was off. I had the ignition module replaced a couple of weeks ago because the truck died and had to be towed. Was told it was the ignition module. It was up and running and a week later the idle went up and the check engine light came on again. It's not idling like this all the time - just here and there. Also if the truck sits for more than a day the battery seems to drain and it needs to be jumped.
I will try below and see how that works out

Thanks
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Tuesday, November 18th, 2008 AT 9:09 AM

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