Too fast an idle speed. If an engine without computerized idle speed control is idling too fast and refuses to come down to a normal idle speed despite your best efforts to back off the carburetor idle speed screw or air bypass adjustment screw (fuel injection), air is getting past the throttle somewhere. Common leak paths include the carburetor and throttle body gaskets, carburetor insulator spacers, intake manifold gaskets, and of course, any of the engine's vacuum fittings, hoses and accessories. It is even possible that leaky O-rings around the fuel injectors are allowing air to leak past the seals. Another overlooked item can be a worn throttle shaft and a defective idle speed speed control motor/valve stuck in the extended (high idle speed) position/throttle position sensor. Also the throttle plate could be binding in its bore and kinked accelerator cable, coolant temperature sensor might not be operating properly misleading the computer that the engine is still cold and computer throwing fuel at it raising the idle speed
September, 19, 2008 AT 12:42 PM
Though what you said is very viable, 5000 rpm isnt a " high idle" my 86 redlined/rev limited at 5500. So this isnt a computer problem.
Even if the IAC was completely ripped out, the tps was bogus, and the o2 sensor was plotting to blow your engine, you couldnt race the car to 5000. The butterfly valve has to be cocked WAY open. Or the throttle body is completely diseengaged from the intake manifold.
I would suggest taking your Throttle body off and inspecting thoroughly for any holes. Also, the throttle return spring, which closes the throttle back down needs to be correct. If there is not spring, the butterfly valve will try and open all the way and not come back.
I would not advise running the car at all until this is solved. Youll end up really hurting the motor at 5k RPMs