I have a 2003 a6 4.2 with a vibration/misfire that my mechanic just can't figure out so i thought I would post it here to sdee if anybody has any ideas or a similar problem. The car runs great when you drive around town but in 4th gear or 5th gear there is a wierd vibration right at 2000 rpm which goes away as soon as the car downshifts. I would think it was something in the driveline if it wasnt for the engine light flashing and also it seems to be RPM dependant not road speed dependant. Also, if you accelerate really hard on a freeway on ramp the car starts to surge and buck at higher rpms and the engine light flashes. My mechanic replaced the coils, MAF, seconday air pump, which were all things coming up in the fault codes but it still has the problem and still has the random misfire fault code. Any ideas?

 

in regards to your issue i have discussed this with my mechanic he says to order a new ignition control module, i will be replacing mine i'll hit u back in the spring it's a very likely fix without even seeing your car, ask around i'm sure youle find this helpful as i know my engine is tip top yet a simple fault in this module will throw false code all day your way

 

I would get a fuel pressure gauge connected & see what the fuel pressure is doing under heavy load.