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・Fair and transparent pricing

Get a quote

What others are asking

Q: My alarm is randomly going off

There are numerous reasons this may be happening. However, there is a technical service bulletin (TSB) #09-BE-026 pertaining to alarm system self activation due to a defective hood switch pad. The TSB states: The vehicle alarm system may intermittently...

Q: 2009 Lincoln MKZ vibrates between 25-40 mph

I would recommend having your wheel balance checked. Often times vibrations, such as those you are experiencing on your Lincoln MKZ, can occur while driving if the wheel balance of any of the wheels is out of specification by more...

Q: What does the Tailgate Open warning light mean?

The Tailgate Open warning light is located on the instrument panel, and will illuminate when the trunk is not properly closed. When the trunk is closed completely, the light will go away. Tip Like all warning lights, the Tailgate Open...

Related articles

How Long Does a Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...
P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...
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.