I have a 99 A6 2.8. I replaced the timing belt and valve cover gaskets and now I get codes P1545, P0300,P0303,P0302. The car will start but barely runs and backfires slightly. Car was running fine before I started. What have I done? I do have the camshaft alignment tool and crank marking is right on the arrow.

 

You have some electrical connection undone or crossed. Or, you have a massive vacuum leak due to an intake hose not connected. Go over it again slowly.

Bob

 

Could I have messed up something with the fuel rail cyl 1-3 when I lifted it a bit to put remove the valve cover? Injectors are plugged in so it looks ok. I also cleaned out the PCV components, which is what started this nightmare,

 

Yes, you could have messed up one of the o-rings that seals the base of the injector to the head. Spray carb cleaner in the area while idling the car. If the idle drops, you have found your problem.

 

It turns out the throttle module needed to be reprogrammed. I had the battery disconnected for a few weeks and the TM didnt reset. Lesson learned, if the repair manual doesnt tell you to disconnect the battery, don't do it! At least not for long periods of time.