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Jim Grant's Tech Tips
99
Ford Expedition, High Idle, Then No Idle
Q:
What would cause a ‘99 Ford Expedition when starting
to go up to 1500 RPM and then drop down and stall? The idle
should come back down to about 850 RPM or so but instead
it will die unless I keep my foot on the gas. But, when
it warms up you will hear the idle go up a little and you
can slowly let off and the idle is fine. The problem does
not occur when the temperature is warm outside.
Eric
A:
First
off, I would suggest checking the minimum idle speed. It
will likely be low due to a build-up of carbon deposits
in the bore of the throttle body and on the throttle plates.
Ford claims to put some sort of magic coating to prevent
this condition. But, that magic seems to wear off fairly
early. With clean throttle plates and bore, the minimum
idle speed needs to be checked and adjusted if needed. Minimum
idle speed is where the engine will idle without the computer’s
involvement. This check and adjustment is performed with
the idle air control motor (which is the thing the computer
uses to control idle speed) disabled. If these base settings
are okay then the idle air control motor itself is a possibility.
These units, when failing can be as erratic as the weather.
With your vehicle the basics must be clean and correctly
set. After that the part that the computer controls is suspect.
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