Chevrolet Repair Questions? Ask a Chevy Mechanic for Answers ASAP
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Dieseling of the engine is caused by a large engine vacuum leak, high enigne idle, or a leaking fuel injector(s). If you open the hood and hear an audible hissing sound, try to locate it and repair the leak. Commonly it is a breather hose from the PCV (Positive Crankacase Ventillation) sysytem, or another leak around the Carburator. You can also identify a vacuum leak with a smoke machine used for leak testing, most shops can perform this type of test for 1.0 hours of labor time. If there is no sign of a vacuum leak, the Idle control Actuator may be stuck or faulty, or the throtle linkage or cable on the Carburator is sticking. You can elliminate the throtle cable scenario by removing the cable from the throtle linkage on the carb and than shutting off the engine. If the engine no longer runs on, than the cable was most likley holding the throtle open. I've also had luck on these using carb cleaner to spray down the butterfly and air horn on the carb, it may be sticky and cauisng the idle to remain higher as well.
Sorry for the delay...do you have an rpm guage or external tachometer? We need to know what the idle speed is so we can proceed. It may be the idle speed motor keeping the idle higher, or even the throtle cable. Have you tried disconnecting the throtle cable yet?