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Q: Why does my car idle out of control?

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My Integra has been idling recently from 850 rpm to close to 2000 rpm back and forth once the car slows down. If I disconnect and reconnect the sensor (tps) it starts to regulate the rpm but after a while it goes back to idling up and down. What is wrong with the car?

My car has 190000 miles.
My car has a manual transmission.

A: Hi, thanks for writing in. This is a common...

Hi, thanks for writing in. This is a common sign of a failing idle air control valve. This is a unit that regulates the air flow into the engine as it is mixed with fuel prior to being injected into the motor. When this is not working properly, it may pick up incorrect readings causing the fuel system to supply too much or too little fuel resulting in the erratic idling you describe. This may also be caused by a vacuum leak which can case an irregular idle depending on where the leak may be coming from. Excess air coming into the intake system (vacuum leak) will cause the engine to surge also as you describe. I would recommend having an expert from Your Mechanic come to your home to diagnose this condition to determine the cause of this.

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