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Q: Car idles at high RPMs

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My car has manual transmission. It has gone around 140,000 miles. I've been having some issues with high idling for more than eight months. When I drive it for a short while, it would start revving at high RPMs, over 2800 while it idles. It helps somewhat if I restart it quickly. This is happening with increasing frequency and at even higher RPMs. The dashboard doesn't show any lights on. What could be causing this?

Idling too fast can be caused by several things. But bottom line is that too much air is getting into the intake manifold. Manifold vacuum leaks are a common cause. Do a visual inspection to check for any vacuum hoses that are broken or fallen off.

There can be several possible causes for this. The intake manifold gaskets may be leaking. The power brake booster can be leaking - pinch off the big vacuum hose to eliminate that. A dirty throttle body can be preventing the throttle plate from returning to its closed position. The Idle Air Controller (IAC) can be sticky or failed. The Engine Coolant Temperature sensor circuit can be faulty making the Powertrain control module (PCM) think that it is freezing cold outside which requires a fast idle. Have the high idling issue diagnosed by enlisting a certified mechanic to visually inspect, test, and scan your car.

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