I just replaced my ECU and my map sensor and now my car is doing this backfiring popcorn sound. When I idle it sounds like its fixing to die yet it stays right on 8grand and doesn't bounce around it just seems to deep like its trying to hard to stay on. When I accelerate it's great though the car is very quick and shifts smooth. The engine only has like 60k and it doesn't leak nor smoke. This is a video of the sounds it makes.

http://www.youtube.com/watch?v=iqkCPZi2jCc

And another...

http://www.youtube.com/watch?v=okeXhy8i6pg

 

Can't watch the video at work, but from what you describe, sounds like your timing may be off, best way to check will be to pull your valve cover, and rotate the engine by hand to TDC, and check that everything lines up.

 

Thats what I was thinking...

 

Your valves sound like crap.

Check compression in each cylinder first, than check your timing