By May 5, 2008 Read More →

Vibration at Idle with A/C On

Dear Austin,

I am really frustrated as the garages I went to do not have a clue on my problem.

“I am driving Toyota with 80,000 miles. The car is automatic drive. When I shift the automatic transmission to D, N, R or P mode and the AC is off the sound/response of the engine is ok.

But while the Brake being applied, the AC is on and if the automatic transmission is shifted to D or R then there is huge vibration!!! The vibration is little less if the automatic transmission is shifted to P or N. When the automatic transmission is on D or R mode and the Brake is released the vibration suddenly increases but disappears as the car moves on”.

Pls help.



Hey there Suman,

The first thing I would check if you came to my shop would be your Throttle Body, and we would clean it as needed. The throttle body is basically in charge of regulating the amount of fresh air that enters the engine. This part can become dirty and the moving parts inside can stick, causing erratic idle speeds, dying at idle complaints and rough idle complaints.

Since the A/C compressor puts more strain on the engine when it is running, the idle speed must be increased to compensate for this additional load on the engine. If the throttle body is dirty and not operating properly it will not increase the idle speed enough, and the idle will be rough….this is the vibration you are feeling.

Here is more about the throttle body, and a link to a picture

Throttle Body Cleaning

Ask your mechanic to inspect and clean the idle speed control motor and the throttle body for you. This should be done as part of routine maintenance ANYWAY. I would charge you about $110 for this repair.

If you still have a vibration after the throttle body cleaning, I would inspect the base idle speed and see if it can be increased just a small amount to smooth out the idle, and I would inspect your engine and transmission mounts for wear.

The engine and transmission mounts are large pieces of rubber that bolt the engine to the body of the vehicle. This rubber can break and wear out over normal use and cause the engine to move around more than it should. This movement will be felt in the cab of the vehicle as a vibration and the steering wheel will sometimes shake as a result of these worn parts.

This repair is more costly, so rule out the other two suggestions I mentioned first. Hopefully a throttle body and idle speed motor cleaning will resolve the issue.


Austin Davis

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Austin Davis, consumer car repair advocate. "Hi there! I love to help people solve their car repair problems and I hope my site was helpful to you today. Thank you for stopping by."

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