I have a 2001 audi a6 2.7t. The car was chiped right at 59,000 miles by APR TUNED. I also replaced the faulty throttle body boot with APR'S bi-pipe. However, I have been having problems latley. I took the car back to APR and they said the problems were not caused by the chip. There are several problems I am dealing with. First, the car hesitates at 3,000-4,000 rpm's. When it has dones this, it usually throws codes. The two codes that it is throwing are as follows: random multiple cylinder misfire, and manufactured controlled fuel/ air metering. During this rpm interval boost normally drops then rises again. Does anyone have any ideas on what could cause this? The spark plugs, diverter valve, and mass air flow are new.

Sorry I posted this in the C6 platform forum. The car is obviously c5.