High Idle When Starting (4.0L)
The idle air control valve requires cleaning periodically or else
the engine revs very high on start up.
The valve is located on the front of the throttle body (looking
into the engine bay from the front) to the left of the throttle
position sensor. There are just a couple of Philips screws
holding it on. When it's off, I just wipe off the cone end and
clean the hole it covers.
When the revs are high on start up and it doesn't idle back down
I usually find that there is a glob of oil/carbon or something
preventing it from closing the air bypass hole.
- Jamie Lawson