I have a 97 Z28 with an LT1. I have to push the petal to the floor to get it to start, then it runs rough for a few minutes and stalls out. It dropps rpms, then it revs about 2,000 RPM by itself. I have replaced the hermonic balancer, opti-spark distributer, spark plugs, and water pump. then drove it one time, doing this. it was fine at first then started stalling after about 5 miles. could this be a bad sensor or mass air flow?