I have been having problems with my 91 F150, 5.0 5 speed, the idle goes to 3000 when I put the clutch in then slowly returns to a normal idle, it does not matter where the ac control is set or off. I have replaced the TPS sensor and cleaned the throttle body completely, removed the crank case ventlation stuff and cleaned it up. still I have the problem, I do not think I have a vacuum leak altough I guess that is possible, sometimes the truck runs perfect but most times it wants ti idle fast then slowly come down to normal. Any ideas?
Thanks, George

 

Might be the idle air control is stuck leaving air behind the throttle plates. It's the thing between the throttle plates to the right. May be carboned up.

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97 Lariet-sc-4.6-4x off road-auto-3.55 LS-
superchip-K&N-3"
pvc air box mod-Granetelli MAF