I have a 1990 Oldsmobile Cutlass Ciera with a 3.3L V-6 engine in it , that backfires through the throttle body while trying to start, if you crank it over and hold the accelerator pedal to the floor it'll eventually start, it'll idle rough but if you speed the engine up it'll smooth out. Also if you put it in drive, hold the brake and press the accelerator down it'll go " pop pop pop " The car has 218,000 miles on it and it has a clack clack clack noise coming from the passenger side of the engine. Could it possibly be the timing chain bad or has the timing jumped?