Q: Car vibrates/shakes when sitting still in idle (in gear or in neutral).

asked by on

After having my car serviced for oil change, tire rotation and air filter replacement, as I was leaving the service center my car had a new engine vibration/shake while in park or neutral in idle. If I rev the motor to 1000 rpm the problem seems to go away. I am not getting any engine codes. I have since replaced all motor and transmission mounts (3 were broken anyway) but this did not make any difference. I have taken the car to Roger Beasley dealership who had it all day and could not discover the issue. It drives fine. Any electrical load while sitting still seems to make the vibration worse. Lights, fan, AC, power windows, windshield wipers, even pressing the brake pedal. This is driving me crazy not to mention making me concerned that something serious is about to happen. Any ideas?

My car has 94000 miles.
My car has an automatic transmission.

A: This sounds as if you have a low idle condi...

This sounds as if you have a low idle condition. I can say your car isn't likely to suffer a catastrophic failure because of this. With a condition such as this, it is normal for it to run rougher when electrical components are tuned on and it is normal for a car to run rough when the idle is to low.

My first instinct here is to clean the throttle body, fully warm the car, connect a scanner, and command the IAC (Idle Air Control) valve to move the idle high and low to see how it responds. 9 times out of ten, I have found this to fix this symptom.

Other things to consider:

Some more advanced possibilities include the MAF (Mass Air Flow) sensor, which is the primary sensor the PCM (Powertrain Control Module) uses to calculate air-fuel ratio. Although, I wouldn't go replacing the MAF without a thorough diagnosis from a certified technician.

I'd consider allowing a certified mechanic to diagnose your rough idle if you decide to get this fixed. You'll have a clear idea of what will need to be fixed after doing so.

Good luck!

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

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: loss of power when driving check engine light blinking at 30 mph just changed manifold intake have p0171 p0174codes

You are having problems with the fuel injection system poppet injectors not opening up or stuck open causing the misfire. You may have a bad fuel pressure regulator or you did not seal the fuel lines into the regulator good...

Q: Possible EVAP leak?

Hello! Typically an EVAP leak will not cause the engine to run the way you described or cause smoke to come from the tailpipe. However, an EVAP leak can cause the check engine light to come on and set a...

Q: Fuel

The Mazda 626 is known for having trouble with the fuel pump. Start by having the fuel pump checked to be sure it is getting continuous power. This can be done by simply turning the key on and listening for...

Related articles

What Causes Hoses to Leak?
While the largest part of your engine is mechanical, hydraulics plays a significant role. You’ll find fluids at work in a number of different areas. Your car's fluids include: Engine oil Transmission...
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...
How to Avoid Back Pain in a Car
If you have back problems, sitting in a car for an extended period of time can be excruciating. Even without back problems, you could experience discomfort and soreness from...