Engine running rough or misfiring can be cause by the following:

http://www.2carpros.com/articles/engine-misfires-or-runs-rough

1.Defective spark plugs
2.Inadequate spark/coil,defective spark plug wire.
3.Lack of compression
4.False air leakage.
5.Faulty fuel injectors.
6.Insufficient fuel pressure.
7.Contaminated fuel.
8.EGR valve that is leaking.
9.Oxygen sensors.
10.Throttle position sensor.
11.Manifold absolute pressure sensor
12.Mass Airflow Sensor
13.Idle air control valve

Note: If it doesn't apply disregard it-

Answered by rasmataz
68 questions asked

changed plugs,wires,ignition coils, and modual, MAP sensor, MAF sensor, changed Injectors everything! i put a spark tester in between the plug and the wire and good spark all around still says number 5 cly! when u drive it its great all the way up until overdrive, once in it shakes real good till about 65 then u can barly notice it I am SO CONFUSED! i am VERY knowledgeable with ALL GM cars and trucks and this is honestly a first!

Response from heise123
1 question asked

I have a 96 SSei, transmission done 2 years ago because it started to jerk in OD, so thought it was tranny. 2 years later, internal harness burned out and replaced all solenoids incl. TCC. Also have New TPS and idle control sensor. When it hits OD, it jerks and when I accelerate hard, the engine light flashes. The tranny shop says it's not the trans work done, but that the car is missing???

Answered by pberthoty
0 questions asked