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Q: High idle after throttle body cleaning

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I cleaned my throttle body with carb cleaner about 5000 miles ago. My car used to idle at 800 rpm, but now, when the engine is cold, it idles at about 1500 rpm, going down to 800 as the engine warms up. I've heard people write that this is a normal cold-engine idle speed, but it wasn't like that when it was new, and I don't like the car's driving characteristics from 0 to the first couple of gear shifts. I tried disconnecting the battery to reset the ECU, but that has had no effect. Is there any way I can get its idle speed back down to ~800?

A: Hello, the idle speed on your car is contro...

Hello, the idle speed on your car is controlled by the computer through the throttle body motor assembly. Depending on what the desired idle speed is the computer will move the throttle plate until the engine reaches the desired RPM. In a lot of cases, if you recently cleaned out the throttle body and this occurred right after it is because there is still debris in the throttle bore causing the plate to not move smoothly.

It is best to remove the throttle body and clean it fully on the front and rear of the bore. Once that occurs, the computer should be able to identify the positioning of the throttle plate and adjust the idle after driving for a while.

If the problem persists, then the throttle motor or throttle position sensor may have been damaged when the cleaning occurred. This can happen if the throttle plate is opened and closed over and over again at a rapid pace. A computer scan tool would then need to be used to monitor the inputs of the throttle motor and the throttle position sensor to see what is going on. One other item to check is the air intake tube.

If it was not reinstalled securely, then it can allow excessive air to enter the engine which can also cause it to run like this. If you are unable to find the problem, then I would enlist the assistance of a certified mechanic, like one from YourMechanic, to pinpoint a fix to your issue.

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A: The idle is going to be high at first until...

The idle is going to be high at first until the computer relearns the idle again. Cleaning the throttle body allowed more air to enter the engine, and the computer is compensating by adding more fuel. The idle will relearn if you put the vehicle in drive and allow the idle to come down with all accessories off for about two to three minutes. Then turn on your a/c with blower in high position for three minutes. This should fix it. If this doesn't help, I recommend having a mechanic, such as one from YourMechanic, inspect your vehicle for you.

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A: Hello. It is completely normal for cars to ...

Hello. It is completely normal for cars to idle highly until warmed up. Though on your particular vehicle high idling will likely be caused by a dirty idle air control valve, or carbon buildup on the throttle plate. The idle air control valve will be partially cleaned when cleaning the throttle body. But, it is extremely difficult to fully clean the idle air control valve without removing it from the throttle body. I recommend to remove the idle air control valve from the throttle body, clean it, and also clean the throttle plate. That should help with the high idle. Though again, it is normal for cars to experience high idle until it reaches operating temperature. If you need further assistance, I recommend you have a certified technician, like one from YourMechanic, diagnose the high idle issue and replace any failing parts.

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