How do I fix an Engine has high revs while idling?

Answer 1

The question is too vague to give a specific answer, however; a high idle can only be caused by one basic problem: too much air is getting into the intake manifold. Now, this can only be caused by one of (or any combination of) three things.

1. Throttle. If the throttle cable is too tight (likely) then it will always have the throttle open somewhat. Or, if the throttle is get stuck (not very likely at all) it will be open as well.

2. Vacuum leak. If any gaskets related to the intake manifold (IACV gasket, throttle body gasket, etc.) lose seal, or if any hoses or tubes (brake booster line, fuel rail ventilation, etc.) are disconnected or damaged, then too much air will get into the engine. This is easy to find, as there is usually a loud hissing coming from the source of the problem.

3. IACV malfunction (most likely). The idle air control valve is a solenoid operated plunger that regulates air into the engine when the throttle is closed in order to keep the engine running. If you have a check engine light, pull the code to be sure it's for the IACV. If it is then here are the two possible problems. One thing that is extremely common (especially on high milage cars) is that carbon will build up and cause the valve to stick. In this case it is worth while to clean it with a degreaser and then reinstall it and see if the problem improves. If this doesn't work then it's probably a malfunctioning IACV and you'll likely have to replace it (don't forget a new gasket!). I think this part ranges between $100-200.

I replaced the Idle Air Control valve on my 1990 GMC Truck, 4.3 liter engine in Feb 2010. The cost was $24.95 at Autozone. I am sure that the price varies with the Automobile type.

When I start my truck the motor idles very high and even when it is at normal operating temperature it does not change. The AIC did not help. I will have to see if it is vaccum leak.