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Discussion Starter #1
Hey everyone,

I bought my used 2006 Colorado about 4 years ago (75k miles). It now has 109k miles and is in terrible shape :( . It started ever since I brought my truck to my mechanic for a tune up. It was starting to run rough so I knew this truck needed new spark plugs and a throttle body cleaning. The truck ran much smoother after that even though I noticed that it was idling a little higher than normal. About a week later, the engine started to misfire only at idle. Sometimes it was just a small misfire and other times it would start shaking the truck. The second week after the tuneup (this week) it got much worse. It would misfire while driving and would almost stall at idle.

I was fed up yesterday and decided to bring it back to my mechanic and see what was going on. They looked at it for 2 hours and then came to the conclusion that my timing chain may need to be replaced but they wouldn't know for sure until they took the front part of the motor off (est. 9 hour job $1,000+). Apparently this issue is a known problem with these trucks (I wasn't aware of that). They pretty much told me that the truck was shot and that they could give me a ride home if I needed it.

I was in the market for a new vehicle but I didn't expect my Colorado to just go out like that. Should I get a second opinion? Has anyone else had this issue?
 

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P0304 is Cylinder #4 Misfire - not timing related unless you had other codes cam/crank codes. A compression test on each cylinder would be a good option rather than pulling the front cover (a lot easier) and would give you a good idea if it's head related like a few other members have had.
 

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Discussion Starter #5
Yes, it started running bad after they replaced the spark plugs and cleaned the TB. The code disappeared after it left the shop and it actually ran pretty good on the ride home. Today, however, it is misfiring again.

Timing problems don't come and go like that so in a way, I think the shop was just tired of dealing with it.
 

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You took the truck to the shop for a tune-up, so I'm assuming that you cannot work on it yourself, for whatever the reason. If you can, find another shop, or even a friend, and have them re-accomplish the tune up, checking the spark plugs an coils for correct installation. If you did not have the problem before the work, something the mechanic did, most likely caused the problem. These trucks like ACDelco Iridium plugs which should not be "gapped" when installed. The coil installation can also be a bit tricky. If everything checks okay, have the #4 coil swapped with #3. If the coil is bad, you will get a P0303. Don't let anyone start ripping and tearing at the engine until you have eliminated all of the external possibilities.
 

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Discussion Starter #7
I just haven't had time to mess with the truck lately. I thought that a skilled mechanic would be able to complete this task with ease. I know for a fact that they installed Bosch Platinum plugs.

It ran rough again this morning but no code or pending codes.
 

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I just haven't had time to mess with the truck lately. I thought that a skilled mechanic would be able to complete this task with ease. I know for a fact that they installed Bosch Platinum plugs.

It ran rough again this morning but no code or pending codes.
That could be your whole problem because those Bosch platinum plugs are complete junk imo.

I would install a new set of AC-Delco Iridium Plugs with the SuperSparkz spring delete upgrade.
 

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Swap the coil to another cylinder and see if the misfire follows. If it does you have a bad coil. Get iridium plugs our coils don't seem to like anything else.
 
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