Has the topic of intermittant fast idle between shifts ever been addressed.... seems my '96 4WD 300-6 FI works fine 90% of the time... then out of nowhere, I will shift from one gear to another... makes no difference which and the throttle sticks at whereever it was in the last gear... FAST usually... this fast idle will slow down after a few seconds on its own... it is like a sticking dashpot in the older carbureted engines... though I don't see one on the FI????

 

Sounds like the Idle Air Bypass Valve is sticking or a little slow to respond. It controls normal idle speed, fast idle (choke or A/C), and acts like a dash-pot during deceleration. My engine started to hunt for idle and it turned out to be a bad IAB valve. They tend to get a little residue build up so you might try cleaning it first. Hope this helps.

 

The IAB is located on top of the throttle body. It is a small cylindrical housing with an electrical plug attached.