Q: Why does my car vibrate when idle?

asked by on January 17, 2017

My car was driving fine last night. I put premium gas in it last night as always. Then this morning when I pulled out of the garage, it started to putter/shake at a very slow speed. I put the car in park and it didn't putter. It only putters when I begin to accelerate, and when I'm idle but still in drive. What could it be?

My car has 93712 miles.
My car has an automatic transmission.

Hi There, It sounds like you may have a dirty or failing idle air control valve causing your engine idle to fluctuate and eventually stall. The idle air control valve is a small valve on the engine’s intake system that reads the air intake as it comes into the motor. This is controlled by the car’s ECM which uses this information to make adjustments to the air/fuel ratio depending on various inputs such as outside air temperature, intake air temperature, load and various other things. As you accelerate, your car’s engine is receiving a much higher dose of fuel than when at idle and conversely, when you let off the gas pedal, there is a sudden change in this fuel supply as a result of your foot letting off the pedal. When this happens, the job of the idle air control valve is to bring this deceleration down to a slow and smooth idle rather than suddenly cutting off the fuel supply causing the motor to die. When the idle air control valve is not working properly, this cause a disruption in this process resulting in the engine not being able to idle properly. I would recommend having a professional come to your location to diagnose and inspect your vehicle.

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