Rick's Free Auto Repair Advice

Posts Tagged: high idle

How does an idle air control valve work

What is an idle air control valve Many people are confused about how idle air control valves work. An idle air control valve literally bypasses air around a closed throttle plate so the engine can get air at idle. Because it bypasses air, it’s also called an air bypass valve. Back in the days of carburetors, idle speed was adjusted by way of an idle speed screw. In fact, on many carburetors there were two idle speed adjustment screws; one for hot idle and another for cold. Turning the screw … Read More

Bad idle air control valve

Bad idle air control valve symptoms Idle speed goes up and down or high idle First off, this is a fairly common problem for all makes and models. Sometimes the problem is caused by a gummed up or sticking idle air control valve (IAC) or a dirty mass airflow sensor (MAF). But it can also be caused by a vacuum leak. How an idle air control valve works If you’re familiar with older carbureted cars you remember that you turned a screw to set the idle speed. The screw turned … Read More

Should you get induction service?

Is induction service a rip off? Shops recommend induction service for customers, even though it’s not listed in the car maker’s maintenance guide. Induction service can also be called fuel induction cleaning or air induction service, but it all means the same thing. What we’re talking about here is cleaning the air cleaner box, ductwork, and the throttle body. Some shops also spray an upper cylinder cleaner into the intake to clean carbon off the valve stems. Cleaning the air filter box is supposed to be part of the air … Read More

High idle, rough idle

What causes a high idle, rough idle Diagnose and fix high idle or rough idle Any time you see a high idle, rough idle high, or hunting idle, it’s time to suspect a vacuum leak. Extra air leans out the exhaust mixture, which is detected by the oxygen sensor and reported to the powertrain control module (PCM). To correct the lean condition, the PCM adds fuel. The extra fuel and extra air are the equivalent of pushing down on the accelerator. As the engine speeds up, the PCM notices that … Read More


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