I have a 2002 Audi A4 1.8t Quattro and here is the problem. My car starts fine a runs perfect, but once it warms up, it either dies or drops rpm's and goes into limp mode. If it dies, it will start back up but you have to crank it over quite a few times. The codes I am getting are o2 sensor, and also a code showing that there is no single from the crank angle sensor. Any ideas?!?

 

The only ideas i can really think of would be maybe an o2 sensor, and maybe the crank angle sensor... ODBII is an amazing thing.

Has your coolant flange been replaced? If so was the temp sensor in the flange replaced? If not maybe start there.