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I have a 2002 Envoy XL. The engine light came on and the engine began to miss badly. I had my buddy who is a decent "old school" mechanic take a look at it. He ran a diagnostic test on it and it show that "cyclinder 1 was misfiring". He suggested I take it up to Advance Auto and get their free diagnostic to confirm. I did and got the same diagnosis. So my buddy took it apart at the coils and said they were all firing but he demonstrated to me that the throttle body was not opening when you gave it gas. He said I probably would need a new motor for the throttle body but that there was some electrical signals that might send a message to the throttle body not to open such as the drive train, etc. Can you help me with this? Thanks in advance.  

if that is the case there will be a check engine light on for this concern with a code for tps not matching...these vehicles are known for injector and coil issues...make sure that you have the proper KV at the coil output

Nick
ASE Master Auto Technician, L1  
ASE Master Auto Technician, L1, ASE Certified Service Consultant, ASE Certified Parts Specialist, Chrysler Certified Service Manager/Technician

Thanks for your response, according to my buddy the coils are all firing. But as he demoed to me when you press on the gas pedal the throttle body will not open. I visually saw this. So this is the first problem. The code from two testers shows "cyclinder one misfiring" so should we try to solve the throttle body problem first?  

Maybe I didn't read your answer well enough. Are you saying there would be a code that should read that the throttle body is not opening and if there is not(no code appeared when Advance Auto also tested it) that there is another problem causing this. Thanks in advance.  

dont worry about the throttle body there is nothing wrong with it. if you had an issue with the tb would you have a problem with all the cylinders. verify commpression, fuel, and good strong spark.  

Thanks, I got in the vehicle yesterday and all was well. The engine light did not come on and the vehicle did not miss. Now consider that it did this for three days and when you stepped on the gas pedal, the throttle body would not open. What give on this? Computer problems? Thanks in advance.  

sounds like a faulty Throttle Position Sensor, however this has nothing to do with cylinder 1 misfiring. To resolve a misfire try replacing the spark plugs and plug wires, If that fails, try replacing the coil leading to the number 1 cylinder. If that stilld doesnt work try replacing the crankshaft position sensor, thats the only thing I can think of for this problem.