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Hello I have a 2004 GMC Envoy 4x4 SLE with the 4.2 inline 6. It’s my wife’s car and when she was driving home today the car started to idle and run really rough. She was pushing the brake and it was shaky and stalled out on her at a red light, it has a smell coming from it I don’t recognize and don’t want to risk any further damage by driving it to the auto parts store for a scan. I recently changed the spark plugs and the BMR(blower motor resistor) I disconnected that just to see and it didn’t change. Has anyone had any issues with this?
 

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2004 chevy trailblazer_lt
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It sounds like you need to clean the throttle body. He is a link the step by step guide posted elsewhere on this forum.


The blower motor resistor pack should not have anything to do with rough idling. As far as the spark plugs go, how many miles between your changing the plugs and the rough idle? About the only thing with the spark plugs would be one or more of the coils not being properly seated on the spark plug, or the electrical connector to one or more of the coils not being seated properly.

By the way, have any codes been set?

Good luck!
 

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It sounds like you need to clean the throttle body. He is a link the step by step guide posted elsewhere on this forum.


The blower motor resistor pack should not have anything to do with rough idling. As far as the spark plugs go, how many miles between your changing the plugs and the rough idle? About the only thing with the spark plugs would be one or more of the coils not being properly seated on the spark plug, or the electrical connector to one or more of the coils not being seated properly.

By the way, have any codes been set?

Good luck!
Hey thank you! I’m going to clean the throttle body today and I started pulling my plugs to see an build up or anything and my number 5 coil pack came apart on me so I’m fairly sure that’s the issue, but I’m going to just clean up everything as I can. Thank you so much for your input that really helped
 

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Hey thank you! I’m going to clean the throttle body today and I started pulling my plugs to see an build up or anything and my number 5 coil pack came apart on me so I’m fairly sure that’s the issue, but I’m going to just clean up everything as I can. Thank you so much for your input that really helped. I also changed the plugs on the 6th of March. I think less than a 1000 miles on the new plugs
 

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Glad to be of assistance. Yes, not that many miles on the plugs for them to be causing problems - unless a defective plug from the factory. Sounds like you found your miss problem what with the #5 coil coming apart. Be sure and replace it with a good quality coil and not a "cheap" no name ebay special.
 

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Glad to be of assistance. Yes, not that many miles on the plugs for them to be causing problems - unless a defective plug from the factory. Sounds like you found your miss problem what with the #5 coil coming apart. Be sure and replace it with a good quality coil and not a "cheap" no name ebay special.
Okay so I replaced the number 5 ignition coil and started it up and now it’s throwing the P0306 code which says it’s a cylinder 6 misfire. I pulled the plug and it has some oil on it and I’m starting to believe either my piston rings are shot or the valve guides are shot. Has anyone had this issue?
 

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A couple of things. First, what part of the spark plug is oily - the insulator, the threads or the electrodes? Second, a compression test might be in order for the engine if it's the electrode portion that's oily. Third, has it been burning any oil?

Are you/your wife the original owner? How many miles on the engine? What is the service history?

Lastly, try switching the #6 spark plug with a another cylinder and in 1000 miles, see if the "new" #6 plug is oily. If it is, and the compression is OK, then perhaps the oiliness is due to leaky valve stem seals. When you start the Envoy, does it emit a bluish cloud of smoke out the exhaust first thing? If so, then that's a sign it could be due to leaky valve stem seals. If you have a continuous emission of blue smoke while running, then it could be rings. Hence the need for a compression test.
 

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A couple of things. First, what part of the spark plug is oily - the insulator, the threads or the electrodes? Second, a compression test might be in order for the engine if it's the electrode portion that's oily. Third, has it been burning any oil?

Are you/your wife the original owner? How many miles on the engine? What is the service history?

Lastly, try switching the #6 spark plug with a another cylinder and in 1000 miles, see if the "new" #6 plug is oily. If it is, and the compression is OK, then perhaps the oiliness is due to leaky valve stem seals. When you start the Envoy, does it emit a bluish cloud of smoke out the exhaust first thing? If so, then that's a sign it could be due to leaky valve stem seals. If you have a continuous emission of blue smoke while running, then it could be rings. Hence the need for a compression test.
A couple of things. First, what part of the spark plug is oily - the insulator, the threads or the electrodes? Second, a compression test might be in order for the engine if it's the electrode portion that's oily. Third, has it been burning any oil?

Are you/your wife the original owner? How many miles on the engine? What is the service history?

Lastly, try switching the #6 spark plug with a another cylinder and in 1000 miles, see if the "new" #6 plug is oily. If it is, and the compression is OK, then perhaps the oiliness is due to leaky valve stem seals. When you start the Envoy, does it emit a bluish cloud of smoke out the exhaust first thing? If so, then that's a sign it could be due to leaky valve stem seals. If you have a continuous emission of blue smoke while running, then it could be rings. Hence the need for a compression test.
We are the second or third owner I believe and it has about 169,000 miles on it. No blueish smoke blowing out of it, I checked and made sure. I started it cold and when it warmed up, had my wife take the RPM to 2500. I replaced the spark plug in the number 6 cylinder and today I’m going to swap the ignition coils 2 and 6 to see if that makes any difference
 

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OK on not being original owner. Also, OK on no blue smoke - that's a good sign. Yes, do swap #2 & #6 coils to see if that makes a difference. Hope it does and solves your problem.

Good luck!
 

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I was just having similar symptoms with my '07 4.2. Had misfire on #6, replaced coil, then random misfires, changed spark plugs (which honestly needed done regardless), still rough idle on cold starts, stalling. Ultimately, my problem was due to a vacuum leak at the intake manifold. A $20 trip to Walmart got me the materials to make a DIY smoke machine to help me identify that I did indeed have a leak, and where it was coming from. You can YouTube plenty of videos on this. You can also try carb cleaner, but it has a fire risk, and you may not be able to spray all the areas where you could have a leak.

Maybe your #5 came apart because it was bad, maybe it came apart because of a lack of dialectric grease when it was installed.

My codes started with the #6, then random misfire, eventually this was accompanied by a lean condition. From what I learned researching my issue, there are a lot of causes for the symptoms I had, and you're having. All this is to say there is a cheap way to eliminate a possibility before you throw money at part swapping.
 
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