I just bought a 99 a6 avant quattro 2.8 automatic, car cranks over however when it finally fires up it sputters and slowly goes up to normal idle, i read that it could be the temp sensor so i replaced that and now it seems to do it everytime i start the car warm or cold, before it seemed to only do it after it had been ran and sat for a while. Any thing would help. Thanks

Are you using good fuel? I had bad fuel once that cause a lot of starting issues.

well i just bought the car a few days ago so i have not gone through much fuel, i put some low grade in it as the fuel door said unleaded fuel only, then i used some mid grade last time i got some fuel so, am i supposed to be running premium in it?