Mechanics

CHEVY

1988 Chevrolet Truck

Engine Performance problem
1988 Chevy Truck V8 Two Wheel Drive Automatic 256000 miles

My truck is idling very high even though I have replaced the Throttle Position Sensor and the Idle Air Control Valve.

The throttle body was rebuilt a year ago.

Rick
Avatar
Richardpm
October 14, 2008.




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.

Tiny
Rasmataz
Oct 14, 2008.


AD