1998 Ford F-150 High Idle RPM

1998 FORD F-150
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HUTCH4
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  • 2 POSTS
I've just installed a tachometer in my 1998 F-150, it's a 4.2 l v6 five speed standard and I found that the rpms at idle are around 1500 rpm. How can I bring the rpms down and at what rpms should it be? Thank you very much. Hutch.
Aug 22, 2006 at 10:19 AM
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MIKEYBDMAN
  • ✓Experienced Mechanic
  • 623 POSTS
[quote:a21f36f268="hutch4"]I've just installed a tachometer in my 1998 F-150, it's a 4.2 l v6 five speed standard and I found that the rpms at idle are around 1500 rpm. How can I bring the rpms down and at what rpms should it be? Thank you very much. Hutch.[/quote:a21f36f268]

Should be 680-830 when warm. The idle speed is not adjustable.
things that can cause high idle.....Vacuum leaks, throttle plate and linkage, speed control linkage binding, intake air tube leaks, intake manifold, and itmes attached for leaks, such as EGR, and IAC.
If not leaks, I would suspect a bad IAC valve.
Aug 22, 2006 at 10:41 AM
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Suggested Repair

Warm idle should be 680-830 rpm and is not adjustable. Check for vacuum leaks, a sticking throttle plate or linkage, binding speed-control linkage, intake air tube or manifold leaks, and leaks at the EGR and IAC. If no leaks are found, suspect a faulty IAC valve.

Conversation Summary

The owner of a 1998 Ford F-150 4.2L V6 with a five-speed manual installed a tachometer and found idle around 1500 rpm, asking how to lower it and what the correct speed is. The expert said warm idle should be 680-830 rpm and is not adjustable. Possible causes include vacuum leaks, throttle plate or linkage problems, binding speed-control linkage, intake air tube or manifold leaks, and leaks at attached components such as the EGR and IAC. If no leaks are found, a bad IAC valve is suspected.

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