hey i just finished doing a complete swap from a v6 to a z28... i swapped everything down to the interior... When i started it up it ran okay. I took it for a little test drive and if i gave it anymore then half throttle it would back fire. It is also idling at 2000 and i can't get it to go any lower. If i put it in gear and let it roll forward then use the brake to slow the engine the car starts to lurch.

The Exhaust manifolds are on then it goes to the cat and just dumps out, i have no muffler on yet... could that cause a problem?