2005 gmc envoy my engine light comes on and stays on for a day or two. I had a diagn. where it showed code for cyl 5 misfire. I was told that I have 6 coils and my mechanic only replaced one (1) becuz of it being so costly and I may only need that one replaced. Removed & replaced all the orginial spark plugs & #5 ignition coil. My light didnt come on for a few weeks but now it comes on and off again. It is also idling high and it shuts off after I am sitting at a light(traffic). My trottle body was cleaned, reset & idle relearn. Can you please help me! Thank you

When was the last time you changed spark plugs/wires? That's the first thing you should check

You will need to have it scanned to get the code, sounds like an engine misfire. Most large chain autoparts stores will scan the computer for free and tell you the code

have the car scanned again, it sounds like you are still having a misfire. if that is the case, take it back to the repair shop and demand satisfaction because they missed something.

you need to repair no 1 cyl. misfire it will misfire when engine load is present. if you want to test it .push brake pedal engine running and shift into forward gear and with the other foot raise rpm to 2000rpm you will feel the misfire
hope it helps

2002 Envoy sle 4.2 L straight 6. Random misfire(PO300). After erasing codes for several days, I finally took my car on the highway and ran it at high speed(70+) for about 4 to 5 miles. Check engine light came on as before but this time it gave me(PO305). Random misfire cylinder 5. So I switched coil 5 with coil 2. Went back out on the highway and repeated as before. This time it gave me(PO302). This was telling me I had a bad coil. Replacing one coil pack solved the problem. The professionals told me low fuel pressure would not give me random misfire, but rather a O2 code because the engine is running lean. Thank you------------------------------------ thank you very much.

First thing to do is clean the throttle body, make sure to clean both the front side and rear side thoroughly. Also, disconnect the battery while doing the cleaning, this will reset the computer and allow it to relearn to the newly cleaned throttle body.

get the soft ware up grade. and have the coils checked.

Our mechanic said we need to replace the computer! The cost will be $1,000.

It is a coil,a coil boot,or a spark plug causing the problem,of course,there is the posibility that the injector is malfunctioning .But it is most likely the ignition part.

you need to have your gmc computer checked for codes ,since the light is now off,they will have to check history codes for what caused it