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I have a 2008 3.7l Colorado with a low/ rough idle rpm.

Customer Question
I have a 2008...

I have a 2008 3.7l Colorado with a low/ rough idle rpm. rpm's deteriorate in about 30 secs when at a stop. rpms drop from a smooth idle @750rpm's to a rough 600-500rpms. the TB is clean and I have inspected the MAF to make sure there is no build up on the sensor.

Mechanic's Assistant: Does the engine stall right after starting? And what about hesitation or jerking during acceleration?

Acceleration is fine and the engine does not stall out. I did discover that the intake manifold was loos and was causing a huge vacuum leak. but I have tightened the manifold since.

Mechanic's Assistant: Are you fixing your Colorado yourself? What have you tried so far?

Yes. I have been chasing a number of problems over the last 3 months. I have replaced the fuel pump after having a problem with fuel supply. I replaced the throttle body after having a problem with the throttle body position sensor. I recently did a resonator delete mod after finding that the crankcase vent hose was missing and replaced the spark plugs to try and fix the idle problem

Mechanic's Assistant: Anything else you want the mechanic to know before I connect you?

Full history** i first started having issues about 3 months ago. first i had and engine shutter when driving ( at all driving conditions) second i was getting sent into reduced engine power when i accelerated over 40 MPH (this was fixed with a new Throttle body and fuel pump) third was sporadic stalling that was caused by loose VERY LOOSE intake manifold (this was fixed by tightening the manifold) and since i fixed the fule pump i have noticed the low/ rough idling. i did have a code for system lean and EVAP circuit

Submitted: 6 months ago.Category: Chevy
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Answered in 6 minutes by:
12/24/2017
Chevy Mechanic: Dan, Technician replied 6 months ago
Dan
Dan, Technician
Category: Chevy
Satisfied Customers: 25,969
Experience: Independent Shop Experience, 2 Year Automotive Diploma, & Access to Information Database
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Chevy Mechanic: Dan, Technician replied 6 months ago

What were the actual codes you were getting? How long has it been since they set last?

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Customer reply replied 6 months ago
system lean p0171 and p0451 i reset the EVAP about 7 days ago and it has not come back. p0171 was after i did a CAI/ resonator delete. i reinstalled the OEM intake minus the resonator and i have not had any codes since, but prior to this work the engine was still idling rough
.
Chevy Mechanic: Dan, Technician replied 6 months ago

Does it seem like it is idling rough/misfiring or just idling low?

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Customer reply replied 6 months ago
its just idling low. it seems to deteriorate after about 30 seconds or so. when i come to a stop the engine will come to an idle at 750-700 rpm and that is a very smooth idle, but after about 30 second it will drop to about 600-500 RPM and i will start to hear a knocking sound. the oil level is good and i have preformed regular maintenance on it every 3500-5000 miles so i don't think the knocking sound could be a rod knock.
Chevy Mechanic: Dan, Technician replied 6 months ago

Have you tried to do the idle relearn?

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Customer reply replied 6 months ago
i have reset the computer by disconnecting the battery but other than that, no. how do i go about doing an idle relearn?
Chevy Mechanic: Dan, Technician replied 6 months ago

Here is the procedure, let me know if it helps. THanks.

-

https://www.dropbox.com/s/sh8t8xbrlmrftnm/relearns.PNG?dl=0

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Customer reply replied 6 months ago
thank you
Chevy Mechanic: Dan, Technician replied 6 months ago

No problem, if that doesn't help I think you have a vacuum leak somewhere. I'd start by checking PCV hose which is common to leak and if that doesn't help spray starting fluid around intake to see if idle changes if so replace intake gasket. I think when intake was loose it could have damaged gasket. Let me know how it goes, thanks.

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Chevy Mechanic: Dan, Technician replied 6 months ago

Ever get it figured out? Please do not forget to rate answer. Thanks.

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