my motor surges when it is cold then after a few min the idle goes to about 800 rpm and it runs fine what is up with this thing. then some times if i go to take of the thing feels like it is loaded up and then clears out and runs ok. then some times it will back fire when i go to take off. all that this motor has done to it is a K&N and flowmaster cat back.

 

I had the same problem awhile back. For me it was a clogged cat and muffler that decided to break up inside the baffles. Cheap GM crap.