3.7 Rough Idle No Codes - Chevy Colorado & GMC Canyon
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post #1 of 28 (permalink) Old 10-21-2016, 07:30 PM Thread Starter
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Exclamation 3.7 Rough Idle No Codes

I know this is a topic that has been talked about allot, I haven't been able to find a forum that talks about the same issues that I am dealing with.

I recently purchased a 2008 canyon with the 3.7 I5 with 120,000 miles on it. During cold start ups the truck idles rough and I mean really rough, until the secondary air injection pump kicks on which then will smooth out the idle. I have changed the plugs, boots, cleaned the TB, and also recently cleaned the MAF. All the hoses seem to be intact with no noticeable areas of concern. The truck is not throwing a code and the dealership says that they cannot tell what it is without a code. Has anyone had this same issue and if so what was the remedy?

Thanks!
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post #2 of 28 (permalink) Old 10-21-2016, 09:33 PM
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When the engine is first started cold it is operating in open loop status and the ECM is using signals from the ECT (engine coolant temperature), MAP (manifold absolute pressure), MAF (mass air flow) and the TP (throttle position) sensors to operate the engine.

If the temp indicator in the instrument cluster is reading normal, around the mid gauge mark, maybe try replacing the MAP sensor. You can find one at Amazon for about $12. https://smile.amazon.com/ACDelco-126...ype=automotive

Not sure what affect the Secondary Air Pump has on the issue. It is pumping air into the exhaust and only runs for less than 60 seconds. Is the air filter clean?

Last edited by cart7881; 10-22-2016 at 10:40 AM. Reason: To change "closed" loop status to "open"
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post #3 of 28 (permalink) Old 10-21-2016, 10:24 PM Thread Starter
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cart7881 Thanks for the quick reply!

The Secondary Air Pump will come on roughly 45 seconds to a minute after initial startup and will run briefly for 30 or so seconds. The second that the pump kicks on the engine begins to idle normal. Prior to the pump kicking on the truck runs extremely rough and shakes as well as backfires. All gauges look to be in normal range when the truck is first started. Also yes the air filter is clean, I checked it this afternoon. It looks brand new and I'm guessing the dealership replaced it when I bought the truck. Should the Secondary Air Pump come on right as the truck is started? Or is the 45 second delay a normal occurrence?

Last edited by Blake.good; 10-21-2016 at 10:31 PM.
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post #4 of 28 (permalink) Old 10-22-2016, 10:55 AM
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My truck doesn't have the Secondary Air System and the Service Manual doesn't have any information regarding the point at which the pump operates. If you are not getting a fault light when the pump is running, the system is probably operating normally. One thing the Secondary Air System does is to assist the catalytic converter to reach normal operating temperatures faster.

That brings us back to the Open/Close Loop question. I corrected my previous post to indicate the engine is operating in open loop status when cold. When the catalytic converter/O2 sensors reach operating temperature the ECM switches from open to closed loop status and primarily switches to the upstream O2 sensor for the signals it uses to control the engine. The input from the air pump could be triggering the ECM to go to Closed loop. If the problem is only happening when the engine is cold, then it could be related to one of the sensors used by the ECM during open loop operation. That's the reason I suggested replacing the MAP sensor.

If you have access to a good scan tool you can check to see at what point the ECM is switching to closed loop.
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post #5 of 28 (permalink) Old 11-18-2016, 11:00 PM
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Same problem??

I also have a 2008 with the I5 engine, I have about 105K Miles. The rough start only occurs on cold starts, but the weather can be frigid or warm, wet or dry. It is intermittent, some days it starts with no issues, other days it has the rough idle for about 10 seconds, then it steadies out.. I attached my laptop based OBD-II reader and monitored it, the system is in Open Loop, and when it calms down, it's in Closed Loop. This started 2 months ago in September. Back in the spring I gave it a tune-up, new plugs, cleaned MAF, etc. All ran well until September. As previously posted, no DTCs, the computer indicates all is well with the system.

I recorded my dash at startup when it occurred and I posted on YouTube. I didn't touch the gas peddle, all hands/feet off everything.

https://youtu.be/d38ot8uvxi0

Any Ideas? I can just start to disassemble and clean everything, checking connectors, but with no DTC, this is strange..

Regards..
Mike
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post #6 of 28 (permalink) Old 11-19-2016, 02:13 AM
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Originally Posted by Scannit View Post
I also have a 2008 with the I5 engine, I have about 105K Miles. The rough start only occurs on cold starts, but the weather can be frigid or warm, wet or dry. It is intermittent, some days it starts with no issues, other days it has the rough idle for about 10 seconds, then it steadies out.. I attached my laptop based OBD-II reader and monitored it, the system is in Open Loop, and when it calms down, it's in Closed Loop. This started 2 months ago in September. Back in the spring I gave it a tune-up, new plugs, cleaned MAF, etc. All ran well until September. As previously posted, no DTCs, the computer indicates all is well with the system.

I recorded my dash at startup when it occurred and I posted on YouTube. I didn't touch the gas peddle, all hands/feet off everything.




https://youtu.be/d38ot8uvxi0

Any Ideas? I can just start to disassemble and clean everything, checking connectors, but with no DTC, this is strange..

Regards..
Mike
Would you say it idles SLOW and rough? If so clean the TB and if that didn't work I would check into cleaning/replacing the IAC. Oops, just saw the youtube. Yes I'll put my money on the IAC (Idle air control valve)

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Last edited by JScottM; 11-19-2016 at 03:04 AM.
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post #7 of 28 (permalink) Old 11-19-2016, 04:55 AM
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These throttle bodies do not have an IAC. Idle Air Control valves were used on throttle bodies that were mechanically controlled by a cable connected to the accelerator pedal.
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post #8 of 28 (permalink) Old 11-19-2016, 12:30 PM
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These throttle bodies do not have an IAC. Idle Air Control valves were used on throttle bodies that were mechanically controlled by a cable connected to the accelerator pedal.
oops sorry, I had a 2007 5 cyl you would think I would know its fly by wire... maybe TPS sensor. There must also be a motor on the throttle that could be dirty or bad. If you have a scan tool look at the TPS readings when your foot is not on the pedal. The reading should not move, it should stay low like 5% and not change. Autozone shows a throttle body unit replacement for the 5 cyl 2008. Could be that but check the TPS first cause its cheaper. google how to test TPS

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Last edited by JScottM; 11-19-2016 at 12:38 PM.
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post #9 of 28 (permalink) Old 11-23-2016, 10:15 AM
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Same exact problem, my post is HERE

Similar symptoms as shown in the video above (though my truck drops to about 400 rpm once, revs to 1500 rpm once, then levels out at about 1000 rpm or until the secondary air injection pump kicks on)

Copied from link:

Occasionally during start up, my truck will idle rough until the secondary air injection pump turns on (loud whirring noise can be heard from front passenger side after 30 seconds or so). Once that noise is heard, the idle smooths out and operates fine. No CEL's present, never had one. I have done a lot to the truck in terms of routine maintenance, but nothing so far has helped.

In the past 2-3 months (10k miles), I have done the following:
Spark plugs (5) - ACDelco Iridium
Coil packs (5)
Cleaned MAF
Replaced PCV Hose to resonator
Cleaned TB
Replaced MAP
Replaced air filter
Replaced upstream oxygen sensor
Replaced downstream oxygen sensor
Replaced idler pulley
Replaced belt tensioner and new belt
Oil change
Battery check, no problems
CT emissions test - passed

The engine performs great when driving. No complaints when on the road. The only issue is this occasional hiccup when starting from a cold engine. I'd say 1 in every 5 cold starts, the truck has a funky idle as shown in the video above (though not as many drops)

2008 LT Crew 4x4, 3.7L w/ 80,000 miles stock

Last edited by Zexy Magician; 11-23-2016 at 10:24 AM. Reason: Adding more details
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post #10 of 28 (permalink) Old 11-27-2016, 06:07 PM
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Quote:
Originally Posted by Blake.good View Post
I know this is a topic that has been talked about allot, I haven't been able to find a forum that talks about the same issues that I am dealing with.

I recently purchased a 2008 canyon with the 3.7 I5 with 120,000 miles on it. During cold start ups the truck idles rough and I mean really rough, until the secondary air injection pump kicks on which then will smooth out the idle. I have changed the plugs, boots, cleaned the TB, and also recently cleaned the MAF. All the hoses seem to be intact with no noticeable areas of concern. The truck is not throwing a code and the dealership says that they cannot tell what it is without a code. Has anyone had this same issue and if so what was the remedy?

Thanks!
Hey OP, I am expecting a Cam Actuator Solenoid this tuesday (Link here)

Will keep you posted on results as we have literally the same exact problem.
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post #11 of 28 (permalink) Old 12-01-2016, 07:47 AM
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Well, if anyone stumbles upon this thread, the cam actuator solenoid does not fix the problem. Going to inspect my evap solenoid next. Not sure if OP has had any luck, thread might be dead and i'm just talking to myself!
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post #12 of 28 (permalink) Old 12-05-2016, 12:31 PM
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Update time:

Replacing the throttle body, battery, and getting a PCM update has fixed it for me so far.

Autozone says 11.5V on the battery is fine. It's apparently not, got a new one.

My TB was buzzing when I touched the gas pedal and had the key turned to "On," engine off. May require you to place something on the gas pedal (or another person can help), pop the hood, and listen for the buzzing from the TB. I replaced it, truck has way more throttle response (more than any TB cleaning could ever do)

PCM update made my warmed up idle rock solid and tweaked the sensors for EVAP and Secondary Air Pump systems to increase sensitivity to potential problems.

I still need to run the truck through a full tank of gas to complete a "cycle" before forming any conclusions. OP, if you are still alive, wondering if you found any solution yet.
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post #13 of 28 (permalink) Old 12-06-2016, 10:30 AM
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Magician, this is not a dead thread, thanks for your postings.. I'll check my battery voltage, but I'll probably do one thing at a time to try and zero in on the problem.. The PCM update, I presume at a GM shop only? If I do that, I have an intermittent wiper blade activation that occurs at any time, I've read where that is also corrected with a reprogramming. I'll post my results..

Again, thanks for the reply..
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post #14 of 28 (permalink) Old 12-06-2016, 06:33 PM
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https://youtu.be/eomaUvzuCRA

Got a video myself in case you are interested.

The PCM update did not solve the problem in the video, unfortunately. Does your idle problem only come about randomly? Mine seems to happen after 1-3 hours of the truck being warmed up and driven for a while. If it sits for 8 hours, fires right up with no idle problems. Same thing if I make a quick stop. Its that gray area in between that the problem almost always occurs.
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post #15 of 28 (permalink) Old 12-06-2016, 10:05 PM
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Have you cleaned the throttle body?

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post #16 of 28 (permalink) Old 12-07-2016, 08:02 AM
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Found oil on my 5th spark plug, threads only. Might have a valve cover issue.

Last edited by Zexy Magician; 12-07-2016 at 01:08 PM.
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post #17 of 28 (permalink) Old 12-08-2016, 08:54 PM
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Quote:
Originally Posted by cart7881 View Post
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When the engine is first started cold it is operating in open loop status and the ECM is using signals from the ECT (engine coolant temperature), MAP (manifold absolute pressure), MAF (mass air flow) and the TP (throttle position) sensors to operate the engine.

If the temp indicator in the instrument cluster is reading normal, around the mid gauge mark, maybe try replacing the MAP sensor. You can find one at Amazon for about $12.
If the MAP sensor is new, TB new, and MAF is clean, would a faulty ECT sensor cause a rough idle if it were going bad?
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post #18 of 28 (permalink) Old 12-09-2016, 08:37 AM
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If the ECT Sensor is faulty you should see some abnormal indications on the temp gauge. There are also DTCs that would show up if the circuit was bad. As you are chasing a really weird problem, it certainly wouldn't hurt to replace the Sensor. I am not one that favors "shotgunning" parts, but you have already covered pretty much all of the other most likely suspects anyway and there isn't much troubleshooting info available for your issue.

The part number for the Sensor is 12601050. I would not suggest getting one at a Dealer unless you are a relative of them. Dealer price is $39.13. Rockauto sells them for $17.96+ship. You probably can find an aftermarket one at a local auto parts store.
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post #19 of 28 (permalink) Old 12-10-2016, 10:23 AM
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Quote:
Originally Posted by cart7881 View Post
If the ECT Sensor is faulty you should see some abnormal indications on the temp gauge. There are also DTCs that would show up if the circuit was bad. As you are chasing a really weird problem, it certainly wouldn't hurt to replace the Sensor. I am not one that favors "shotgunning" parts, but you have already covered pretty much all of the other most likely suspects anyway and there isn't much troubleshooting info available for your issue.

The part number for the Sensor is 12601050. I would not suggest getting one at a Dealer unless you are a relative of them. Dealer price is $39.13. Rockauto sells them for $17.96+ship. You probably can find an aftermarket one at a local auto parts store.
Yea, that's what sucks about this issue... No CEL, so I need to just cover the basics and hope that it works. At least in my case, many of these parts would have been replaced in the near future anyways.

I did find that I have a leaky valve cover gasket. Plug #5 against the firewall has a light coating of oil on the threads. The plug node looks like oil never touched it and the oil on the threads is quite dry/sticky, but regardless, the gaskets need to be replaced.

At least the ECT is dirt cheap. I think I will do that before the gasket just for troubleshooting purposes. These are the last two things I can think of before just giving up on the problem and living with it, or saving up a couple hundred to just throw at the dealership.

Regardless, the help is appreciated! Thanks
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post #20 of 28 (permalink) Old 12-23-2016, 08:07 AM
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As expected, the ECT sensor did not fix the problem.

Next step is to fix the problem with the oil on my spark plug threads (#5 only). After looking around, it may be a valve/cam gasket issue. Another relatively cheap fix if I do it myself, but I may just take it to a dealership for that work (unless the price is outrageous).

For now, I will just live with it and hope for a CEL to give me some sort of direction. At least with all these new parts, my truck runs like a champ!
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