Skip the auto shop - Our mechanics make house calls

Q: Engine surging while driving

asked by on

Hi Chris, I have a 2008 audi a4 2.0T Quattro with about 181,000 km on it. The problem that I am experiencing is engine surging. The surging is bad when the engine is cold and not at optimum running temperature. The rpm fluctuates up and down and I do feel vibrations as it does that. When warm it's not as bad but it still does it whenever I'm driving and the surging only happens when I'm driving. It feels like the car is being held back and I have no codes or stored codes on the vehicle. Could you possibly shed some light on what it might be? Would the throttle position driving ensure cause something like that which is the pedal sensor and not throw a code? I have cleaned the MAF with no luck and it looked pretty new when I pulled it out but cleaned it anyway. Throttle body is new as well.

My car has 112000 miles.
My car has an automatic transmission.

Hi there. For the engine surging making the rpm’s go up and down could be caused by a defective or stuck idle air control valve (IAC). Check the IAC and see if it’s working. Remove the vacuum line to the valve and see if the engine runs smooth. If the engine runs smooth, then the IAC needs to be replaced. If there is no change, then unplug the harness to the IAC and see if there is power to the IAC. If there is no power to the IAC, then check for resistance from the plug to the IAC to the pins on the ECM (computer). If the IAC is working properly, then the throttle pedal position sensor is not calibrated properly and needs either calibrated or replaced. To calibrate the throttle pedal position sensor, turn on the key with the engine off and push the gas pedal to the floor slowly. Hold the pedal on the floor and turn off the key. Then while holding the gas pedal on the floor, turn on the key and release the gas pedal slowly to the rest position. Then turn off the key. Now the throttle pedal position sensor is calibrated to the correct counts that it should have. If you need further assistance with your engine surging, then seek out a professional, such as one from Your Mechanic, to help you.

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

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: Stuck while shifting from second gear to third gear at high RPMs

Chevrolet has a TSB out about a failure with the pressure plate causing hard shifts. The first thing to check is the clutch pedal level when the clutch is being operated if the pedal goes close to or is touching...

Q: Despite having adequate oil pressure, the warning light comes on dashboard

Hi, thanks for writing in. Having the proper oil and oil level, and having the proper oil pressure in your engine are 2 very different and unrelated things for the most part. Having low oil pressure is an indicator of...

Q: My car idles rough when stopped

This may be a sign of a leaky injector or potentially an incorrect idle air adjustment. A leaky injector can cause a rich fuel condition as it may leak too much fuel into a cylinder not allowing the combustion cycle...

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...
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...
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...