Need some help. My son's 2.8 has developed two issues. It's a stick car. It has developed a slight intermittent misfire, but tonight after starting it cold, if you tap the gas pedal, the idle hangs a bit and drops down slowly. Then twice, I would tap the pedal and the rpm would just race out of control, had to turn the motor off so it would not throw a piston. What could cause this? Throttle linkage if free and unstuck.

 

If your 101 % certain the throttle plate in the throttle body is not hanging open , your very next check/procedure will be to clean and check the operation of the "I.A.C." , the Idle Air Control valve . A search of this site will describe the functioning/cleaning of the IAC and after you do that remember that the "IAC Relearn" procedure is valid for the 3.1 engine only , your 2.8 needing only for it to be cleaned (as well as the throttle body passages where it screws in) and to be reinstalled as the procedure you'll find in a search states (the pintle must be fully retracted into the IAC valve body upon reinstallation) ...