My idle keeps going up and down after starting. Going from 2000 RPM down to 500 (almost stalling). Also while driving the idle will stay up around 2000 for about 20 to 30 seconds after putting the clutch in. The engine was checked for vacuum leaks and none were found. Also a new TPS And IAC were installed. Anything else that could be causing this? Vehicle is a 1987 ShelbyZ with a 2.2l Turbo II.