Why am i having problems after battery change in my Audi A6?

[wizmaster]

when i changed my battery the car starts but will turn off without my foot on the accelerator

I feels like I'm not getting enough power from the car and there is a smoke coming out when i started up

why and where did i go wrong?

[fransisaudi]

Check to see if air filter box is closed tightly.

Secondly check if AFM air flow meter is plugged properly on air filter box neck.

Either of these two preventing car to run smoothly, as it disturb the air intake setting and fuel burn rich and leave plenty of white smoke and carbon. Your exhaust tip must have turned carbon black too from light grey.