My 01 z28 ls1 6 speed idles up and down even after replacing the TPS. Also, smokes black and even spits a little raw fuel. Full length headers, 3 inch pipe and flowmaster 80 series. No cats. Bought the car this way and trying to fix it so I can drive it and retain at least a little fuel mileage. The car seems to run fine aside from these problems. No hesitation on stomping the pedal, idle is smooth up and down, no backfire. Starts easily and doesn't throw codes. Any ideas?