i have a 98 navigator 5.4 that has a low idle in gear 450-500 rpm and in park about 550 rpm, it never stalls but it just seems too low. i notice with all accessories on at night things start to dim, if i rest my foot on gas pedal everything is brightens with a little more rpm. i replaced the iac motor with a new one from ford but that didn't do it. is there anyway to adjust idle, or ant ideas on whats wrong. thanks brian h

 

Did you also reset the copmputer to force it to relearn the IAC function?

Try that first.

Also, checking the accuracy of the indash tach would be a good idea. This can be done with a scan tool.

Steve