up and down idle

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Sep 14, 2002 | 09:05 AM

f150cobrajet

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up and down idle

I have a 1986 F-150 with a fuel injected 302 V8. After warming up, the idle will go and down like someone's reving it. I've tried adjusting the idle screw but it only stops at a too high idle that makes the truck jerk hard when putting the automatic in gear. Since the previous owner junked the smog control stuff and cobbled a dual staight exhaust system with just glass packs, I though that might be part of the problem. I've replaced the wires and plugs also. Anyone have a clue of what it could be?

Sep 14, 2002 | 03:32 PM

brown 4x4

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Joined: Jan 2001

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From: Nebraska

up and down idle

[updated:LAST EDITED ON 14-Sep-02 AT 04:33 PM (EST)]Try cleaning the idle air control valve located on the throttle body. These are known to cause idle problems. Also, I wouldn't mess with the idle screw on an EFI vehicle unless absolutely necessary.

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[font color="green"]1995 F-150 Supercab XLT 4x4 302 M5OD 8' bed [/font]31x10.50's
[font color="green"]1986 F-150 4x4 300 I6 NP435 [/font]Warn hubs, DeeZee bed caps, '96 XLT bench seat, new paint job

Sep 14, 2002 | 04:02 PM

Franklin2

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From: Virginia

up and down idle

After you clean up the throttle valve and IAC control, here's how to reset the idle screw. With it idling, un-plug the wiring connector to the IAC. The truck should slowly die. If it slows but keeps running, the idle screw is set too far open. If it dies quickly, then the idle screw is set back too much. This adjustment gets the throttle back in the ballpark, so the IAC has control over the idle speed.