Q: Vibration at idle and worse with ac on , low rpm, mpg went down and no code, what could be wrong?

asked by on

I have a vibration at idle, and it seems to get worse with the AC on, and a few times when starting the car it sound like it going to die but start to work like normal, my rpm is usually close to the 1 but now it idling at 500rpm due to what I believe is because of the idling issue. Also my spark plugs seem to gets dirty even tho it's new I have no codes. I have replace motor and transmission mount, pcv valve, spark plugs, ignition coil, clean throttle body and manifold.

My car has 102000 miles.
My car has an automatic transmission.

Shaking or vibration may be caused by many different things such as faulty spark plugs, poor fuel pressure or misfires. Other things such as a faulty idle air control valve may cause the engine idle to drop below the normal idling RPM which may also cause the motor to shake or vibrate more than normal. This creates a loss of power that resonates throughout the motor additionally causing other problems with ignition and fuel timing. Anytime a misfire is caused, this causes an imbalance in the motor which will cause the motor to shake or vibrate. Other issues that may cause this type of shaking or vibration might be broken engine mounts or potentially tires that are out of balance or worn improperly. Engine mounts are generally rubber mounted braces that hold the engine in place to the chassis of the car. When these break or become weak or faulty, this may cause the engine to vibrate heavily. When tires are out of balance, as the speed of the vehicle increases, the vibration will become much more noticeable and pronounced. I would suggest having an expert from YourMechanic come to your location to diagnose and inspect your vehicle using a scanning tool which will more accurately indicate what specifically may be causing this.

Was this answer helpful?
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
  1. Home
  2. Questions
  3. Vibration at idle and worse with ac on , low rpm, mpg went down and no code, what could be wrong?

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: Mudguard destroyed under my left front bumper

Hello, thanks for writing in about your 2016 Hyundai Accent. You will be ok driving it around. Your mudguard does not serve a critical function that would otherwise prevent you from driving your car safely. If you'd like some peace...

Q: I have changed the camshaft position sensor, crankshaft position sensor, spark plugs and plug wires and there still is no fire.

Hi there. If there was a spark around the speed sensor as the engine was starting, then there is a major short in the ignition system. Check all of the wiring grounds and make sure that they all are hooked...

Q: One of my front side lights won't turn on.

The front lights will have a dual filament light bulb that will use the same bulb for the running lights and for the turn signal light. If you notice the parking (running ) light does not work in one front...

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...
P0052 OBD-II Trouble Code: HO2S Heater Control Circuit High (Bank 2 Sensor 1)
P0052 code definition HO2S Heater Control Circuit High (Bank 2 Sensor 1) What the...
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...