wierd vibration/misfire 2003 a6 4.2

[mtrain]

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?

[bjas813]

I have a '99 A6 Quattro with around 105000 miles and this same exact problem started with mine about a week ago... At first my dad and i thought the moist weather of the northeastern winter season states had possibly affected the timing system, plugs, wires or coils... I bought brand new bosch platinum 2 for all six cylinders and put 9.4 MM racing wires on... NO DIFFERENCE whatsoever...

HOWEVER.... In the process of removing the old plugs i found that they were absolutely saturated with gas and carbon.... This leads me to think that there is a bad sensor in the air intake... Possibly even the O2 sensor. B/C i have full power and throttle control above 5500 rpm... it's like you said with high gear, low rpm accelerations where i get the vibrating and knocking.... I'm even starting to hear it in the drive axle because driving it so long with no possible solutions has caused the motor to bog down while in gear and when it misfires espescially in the front drive axles they click... ANY IDEAS OR SUGGESTIONS PLEASE......... LET US KNOW....

I'm only 17.... My resources and knowledge on german cars is very limited....

[mtrain]

None of the independant shops I went to could figure it out so finally I had to go to the dealer. Mine turned out to be the motor/solenoid that controls the variable length intake runners.Unfortunately it is an integral part of the intake manifold and they had to replace the whole manifold for $2,500.00. Ouch!

micah