Skip the auto shop - Our mechanics make house calls

Q: Why a vibration is felt when the AC is on during stops on street lights?

asked by on

When the AC is on and I make a stop on a street light, I feel a vibration that seems to come from the engine. The vibration in that situation is not steady. It comes like the waves in the ocean. it can stop for a little while and do it again. When I driving the car I don't feel the vibration. I appreciate your help.

My car has 25000 miles.
My car has an automatic transmission.

A: Hello, thanks for writing in. This vibratio...

Hello, thanks for writing in. This vibration is usually the result of low idle. When loads such as the AC system or a steering wheel turn are placed on the engine, the idle needs to rise to offset this. If it does not, then the engine will begin to run rough. Most of the time this is caused by a dirty throttle body. When the throttle becomes dirty the computer has a hard time trying to maintain an idle. It can also be caused by a worn engine mount so I check those also to try and isolate the problem. I would recommend having an expert from YourMechanic come to your home or office to confirm a diagnosis on the rough idling issue, and make or suggest the necessary repairs or replacements.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Save up to 30%

Get a quote

What others are asking

Q: Car gets very low gas mileage

I would do a little quick research and find out what is typical real-world MPG for others who drive your make and model. That will provide you a realistic base-line expectation that will be more accurate that Mazda or EPA...

Q: Engine vibrates due to bad motor mounts

Hey there, thanks for writing in about your 2003 Geo Tracker. There are a variety of potential causes for the problem you are having. It could be that what you are feeling is an engine misfire. If the Check Engine...

Q: Heat gauge problem

The temperature fluctuation when turning on and off the heat suggests that you may have an overheating issue. The thermostat is a more commonly known part to fail when it comes to an engine overheating. I would recommend having the...

Related articles

Rules of the Road For Iowa Drivers
Driving on the roads requires knowledge of the rules, many of which are based on common sense and courtesy. However, even though you know the rules in...
P2428 OBD-II Trouble Code: Exhaust Gas Temperature Too High Bank 1
P2428 code definition A P2428 trouble code signifies that the PCM has detected a problem in the exhaust gas temperature sensor circuit in bank 1, which subsequently contains the number one...
P2103 OBD-II Trouble Code: Throttle Actuator Control Motor Circuit High
P2103 means there is a fault with the throttle actuator control motor circuit, likely due to a defective electrical component or part.