Engine Performance problem
1996 Chevy Suburban V8 Four Wheel Drive Automatic 134000 miles
JUST BOUGHT A 1996 CHEVROLET SUBURBAN K2500 WITH VORTEC 7.4 V8, I HAVE CHECK AND THERE ARE NO CODES IN THE SYSTEM, DIAGNOSTICS HAVE REQUIRED THAT BOTH O2 SENSORS(UP STREAM), ICM, AND MAP SENSOR BE REPLACED. MY PROBLEM IS THAT EVERY TIME THE VEHICLE IS STARTED THE START IDLE STARTS AT 1800-2000RPM. MOST THE TIME IS WILL SETTLE TO 600-800 RPM BUT SOMETIMES IT WILL SIT AT 1000RPM TIL IT IS DRIVEN A SHORT DISTANCE.I HAVE CHECKED FOR VACUUM LEAKS, REPLACED THE IAC AND HAVE ALSO REPLACE THE EGR GASKET WHEN REMOVED AND CLEANED. THE VEHICLE RUNS GREAT EXCEPT FOR THE STARTING HIGH IDLE.
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.
May, 23, 2008 AT 1:10 PM
An Ohm meter across the engine coolant temp sensor will reveal a bad one, Cold it should read over 100,000 ohms hot 177 ohms.