ADJUSTING RPMS/ / 4.2/ 131,000 MI

1998 Ford F-150

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.
August 22, 2006.

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.