Ford explorer 4.0 1991 high revs
not told hot or cold engine
the controls for idle are not the same , those 2 modes.
how high is high RPM,.
hot is 800 RPM regulated by PCM + isc idle valve.
cold is controlled by IAC,thermal air control valve.
and runs about 1200 to 2000 rpm,cold
cold in Florida is 1200 cold in ALASKA is 2000.
if the thermostat is bad, stuck open, and 150f coolant temp the RPM will be stuck high all the time
as will huge vacuum air leaks, the MAP sensor sees that and engine screams.
pully connectors is useless as doing so puts he PCM in limp home mode and idle controls are disabled in that mode. limp
there are lots more tests, to do. but my fingers are tired.
get shop to fix it?
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