Q: Engine surging while driving

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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.

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