I have a 1990 model Pontiac 6000 le with 3.1 V6 engine.It has a miss and overall rough and low speed idling ccondition..I have replaced plugs wires and coil packs.Checked for fault codes because check engine light came on but none are showing up except code 12 which is the the normal computer fault code.I was going to change fuel injectors since this engine has 160,000 on it.Im wondering about the planum I have to remove.Are there a gaskets that have to be replaced if removed.I dont know what else to check on this engine,Im at my witts end with it.Help Aaron

 

check each plug individually to make sure it is firing, you can use a tester or just hold it and ground it out on the engine and look for a spark.

 

I agree. Check for spark. Before you replace the injectors, do a compression test. A burnt valve or weak cylinder will cause a rough idle or miss. If you think you'll end up replacing the injectors, you'll be replacing the upper plenum gaskets. use your vacuum cleaner because I'm sure you'll have a nest and some leaves under there. Inspect the injector wiring closely. Make sure it is intact. Get access to a niod light set to make sure each injector is recieving a signal. Injectors are expensive. Rule out all else first. Good Luck

 

one other thing... if this miss is just at idle...you may have vacuum leak. Many times it is the PVC hose under the plenum. With the engine running, spray carb cleaner under the plenum, around the intake gasket mating surfaces, the throttle body. Listen for a change in idle for each individual area. If you have a leak, fix it. If the car runs poorly, give it a day of driving to relearn it's idle and other characteristics. If it still runs poorly, take the steps I previously mentioned.