2008 A6 G28 Fault (Incorrect Correlation)
 

Had the Catalyst recall done several months ago and shortly after, the <MIL light came on. The diagnostic indicated the Engine Speed Sensor (G28)and additionally, a second fault, coupling it with the G300 Cam Sensor,
both indicating an incorrect correlation. They return after being cleared immediately, with no noticeable performance impact other than acting a little twitchy at the idle ... Have replaced the both to no avail.....It seems that after being cleared and the MIL extinguishes, it idles in a smooth, normal manner but after I turn the car off, then restart it, the faults and MIL return again along with this nervous idle. Anyone have any ideas...?? I would like to trade it in at Audi for a newer year at some point and would rather this was remedied beforehand..

check the cam adjuster solenoid for any metal mesh stuck in it, had the same fault and this solved my problem.