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Discussion Starter #1
Ok I have a strange problem that has me stumped. I have a 2011 Chevy Colorado with 78,000 miles on it. This only happens when the truck sits for 6 to 8 hours. I start it up and it fires up right away no problem. It runs at 1000 rpms for 30 or 45 seconds. kind of the choke mode. it then drops to around 800rpms 3 seconds later it sputters and almost dies. it does this 3 times in a 30 second period then goes back to normal rpms and runs great! I'm getting 26 mpg it is the 2.9L 4 cylinder fuel injected engine. and its throwing no trouble codes? Its so weird you could probably use a stopwatch and get the same time every time? I have changed spark plugs, cleaned the MAF sensor, cleaned the throttle body, tried a better gasoline and ran seafoam through the system. The battery is strong the air filter is clean and the oil is changed regularly and I see no visible air leaks? nor do I see any fluid leaks and there is no smell of gasoline. If I rev the engine for about 2 minutes at 1500 rpms till it is slightly warm it will not sputter after that. I have looked all over the net for answers and have gotten some good ideas but I have yet to find a solution? Anyone have any ideas? anyone have this same problem? Any help would be greatly appreciated! Thank You!
 

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It does seem to be something related to the "Open Loop" operation. The Service Manual indicates that inputs from the ECT, MAP, MAF and TP Sensors are used to determine air/fuel ratio when in open loop. Maybe check the MAP Sensor?
 

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Discussion Starter #4
I was just wondering why it wouldn't throw a code? Maybe that or a coolant sensor? Now I have a couple things to check. Thank You!
 

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If you continue to have this problem, maybe you could find a scan tool that reads "Real Time Data" and check the sensor readings during first start up. I wouldn't suspect the ECT sensor if your temp readings are normal otherwise.
 

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Discussion Starter #7
I think I found the problem I do have a MX obd link scan tool and I see the coolant temp is 15 degrees higher than the ambient air temp. Guess I will try and replace the coolant sensor. Thank you all!
 

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It is weird that you aren't throwing a code, but it doesn't surprise me completely. Some sensors have a range which even though it's bad won't be far enough out to throw the DTC.
 

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Discussion Starter #9
Well I guess my engine was not cool enough after 6 hours. I rechecked the coolant sensor and ambient air temp and they were about 4 degrees apart. On to the MAP sensor I guess.
 

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Discussion Starter #11
Yes I was hoping its not that. I guess if it is it would still be under warranty. I am going to take it in for a transmission flush and transfer case in a couple of weeks. I will see what they say about this. What a pain. This is a great forum glad I found it. Thanks!
 

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Discussion Starter #12
The dealer seems to think its a sticky valve. Says they have seen this before. Find out in a little over a week.
 

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So yeah I had it in and it was sticky valves. They did a engine top clean that helped a little but not enough. It goes in Tuesday for a valve job. get that carbon out of there. I didn't even realize it was still under warranty. Gotta love that GM 100,000 mile drivetrain warranty! includes a free loaner car.
 

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Interesting you had head problems on a newer truck. They redesigned the valvetrain because up to about 2008 there were a lot of valves leaking down and causing warranty head replacements.

I had 3 cylinders with close to 80% leakdown.
 

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So yeah I had it in and it was sticky valves. They did a engine top clean that helped a little but not enough. It goes in Tuesday for a valve job. get that carbon out of there. I didn't even realize it was still under warranty. Gotta love that GM 100,000 mile drivetrain warranty! includes a free loaner car.
Can you elaborate on the 100,000 mile warranty and reason for a valve job?

You are 100% sure this is a "no cost to you" repair?
 

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Discussion Starter #17
Yes it was covered under warranty. They never had to take the heads off. Problem was fixed. The night before I took it in I had a service engine light come on. Totally different problem. It was a bad solenoid. They fixed that too under warranty. Warranty includes a free loaner car.
 
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