3.7 Rough Idle No Codes - Page 2 - Chevy Colorado & GMC Canyon
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post #21 of 28 (permalink) Old 01-04-2017, 12:30 PM
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Originally Posted by Scannit View Post
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..
When you get a chance, can you let me know if you have a hood insulator?

Wondering if this is some sort of hot soak problem with the winter fuel... All of the forum posts I can find that have the same issue as us were started in the winter. The link below has more details on winter fuel and hot soak, not sure how credible though...

Hot Soak and Winter Fuel
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post #22 of 28 (permalink) Old 01-16-2017, 10:21 AM
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Originally Posted by Zexy Magician View Post
When you get a chance, can you let me know if you have a hood insulator?

Wondering if this is some sort of hot soak problem with the winter fuel... All of the forum posts I can find that have the same issue as us were started in the winter. The link below has more details on winter fuel and hot soak, not sure how credible though...

Hot Soak and Winter Fuel
Hello Zexy, (please don't tell my wife I called someone else Zexy, she'll flip especially since I don't know if you're a guy or girl )

No hood insulator on my truck. But this started in Sept/Oct. I at first thought it may be bad gas, or something else that may be temporary and work itself out. So I took some time before I started posting, which would be in the winter. It made no difference if it was warm or cold (freezing), it may or may not occur.

Regards..
Mike...
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post #23 of 28 (permalink) Old 01-16-2017, 09:02 PM
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Hello Zexy, (please don't tell my wife I called someone else Zexy, she'll flip especially since I don't know if you're a guy or girl )

No hood insulator on my truck. But this started in Sept/Oct. I at first thought it may be bad gas, or something else that may be temporary and work itself out. So I took some time before I started posting, which would be in the winter. It made no difference if it was warm or cold (freezing), it may or may not occur.

Regards..
Mike...
Ha! Fair enough! Call me Bill

From what I have found, all history of this problem in other forums starts when gas stations switch over to winter fuel. Also, it seems to only affect the 08 models. Strangest thing... Oh well, I plan on posting back here in May with an update. If its not the fuel, then maybe the dealership can figure it out. It would be there by now if I didnt have a wedding to plan!
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post #24 of 28 (permalink) Old 03-01-2017, 07:49 PM
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In case anyone with the same problem finds this thread, here is an update:

To summarize, the idle surging only happens in Open Loop mode (disregard the thread title related to the air pump). The problem has never come up when the truck starts cold or hot, but somewhere in between.

For example; I drive the truck to work and it heats up all the way, I park the truck and come back 1-3 hours later, start the truck up again and the idle stumbles/surges in open loop. Idle smooths out once the truck switches to closed loop (after 15 seconds or so). Otherwise, the idle is rock solid and this truck runs like a champ.

In the past 10k miles, I have done the following:
- Spark plugs (5) - ACDelco Iridium
- Coil packs (5) (ACD)
- Cleaned MAF
- Replaced PCV Hose to resonator
- Replaced TB
- Replaced MAP
- Replaced air filter (Wix non-oil)
- Replaced upstream oxygen sensor (ACD)
- Replaced downstream oxygen sensor (ACD)
- Replaced idler pulley (ACD)
- Replaced belt tensioner and new belt (ACD)
- Replaced Engine Coolant Temp sensor (ACD)
- Replaced camshaft actuator solenoid (ACD)
- Tested fuel system pressure, held constant with no signs of leaking injectors (@55-60psi)
- Oil change (5W-30 synth)
- New battery (Group 65)
- Seafoam intake and gas tank
- Identified a battery drain issue with my remote start, removed remote start and unplugged all electronics
- Monitored for pending codes, never had a CEL, no CEL present

If you have the same exact problem I have, the above will not fix it.

To be sure you have the same problem, refer to the videos below. Remember, this problem does not happen every time the truck starts, only after a hot soak. If you experience this idle problem more often than not, I doubt we have the same issue.

https://youtu.be/d38ot8uvxi0

https://youtu.be/eomaUvzuCRA <--Hard to catch, but stumble is at the 5-11 second mark

WHAT HAS HELPED: Gas quality

Since making sure I have only top tier gas in the tank at all times, the problem has been somewhat reduced. Is it eliminated? Nope. Running higher octane fuel has almost eliminated the problem, but at a cost obviously.

Why? Maybe this article about the volatility of winter fuel? After PM'ing a few people across forums (even Hummer owners), every 08 I5 owner I talked to has had this problem once gas stations switched to winter fuel (around September).

So for now, that's my only lead. Wait it out until the spring and hope it goes away! In the mean time, my coolant looks gunky, so I am going to get the fluids flushed/filled this weekend, brake and rear diff included. And who knows... that might just fix the problem!
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post #25 of 28 (permalink) Old 03-08-2017, 12:50 PM
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Zexy (A.K.A. Bill) and others,

I do not know if this is associated with our problems, but I figured I'd pass it on.
I recently got a CEL and the code posted was P0449, which points to the Vent Valve Solenoid problem... 2 years ago, I got a similar code (P0446?) and I had to replace the solenoid assy on the vent box that is located just in front of the spare tire. Today, I accessed the same solenoid I replaced 2 years ago and got out my trusty Harbor Freight multi meter and Ohm'd the solenoid, it was OPEN (infinity)!. When I got the replacement part, I measured it's resistance and it was 20 Ohms, which I would consider normal for this. Now, since my issue with starting is intermittent, I can not state this is associated with the rough start issue. But since just about everything else has been tried under the hood, I figure this may point to something.
As for not getting a CEL if the solenoid is faulty. I presume the computer detects current flow for the solenoid. If the coil resistance has increased to the point where it fails to function (let's say 50 Ohms), the computer MAY detect enough current and not report a faulty solenoid, this is just my theory.
FYI, I'm an electronic repair technician for the semiconductor industry with >30 yrs in the industry. I don't repair cars for a living, but the electronics theory remain the same.

So I would recommend taking a 13mm wrench to the single bolt that holds the canister assy on it's self, directly in front of the spare tire. I was able to swing the canister, with the hard plumbing attached, to access the plug, which is on the passenger side. Unplug the solenoid and see if you have ~20 Ohms. As a sanity check, touch your probes together and ensure your meter and leads are working properly, the digital meter should start at infinity (1.___ on the meter screen) to <1 Ohm when the leads are shorted. Too many times I've forgot to put the meter in the right setting, OR I had a bad meter or test lead.

I recorded my first replacement but I never posted it on YouTube. I'll see about cleaning it up, especially with this current event, and I'll post a link when done. But I added a picture to this post on accessing the assy.. Your connector may differ slightly, at some time, they changed from an Oval connector (pictured) to a more Square connector, but your results should still be the same.

I'll update on the starting performance.

Good luck..

Mike
Attached Images
File Type: jpg Vent_Solenoid_Connector.jpg (301.5 KB, 9 views)

Last edited by Scannit; 03-08-2017 at 04:01 PM. Reason: Clarified diagnosing between 2 years ago (P0446) and Today (P0449)
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post #26 of 28 (permalink) Old 03-08-2017, 03:00 PM
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I have a very similar issue to everyone here- occasional erratic idle when cold that fixes itself by idling higher until it warms up a little (same as in Zexy's videos). I don't have much to offer as I haven't done most of the fixes listed here so that's where I'll start (only had the truck a few months but it only has 36k miles on it).

I did want to mention that I get a faint gas smell every now and then (even with windows rolled up but HVAC set to let outside air in). The smell is not always associated with the erratic idle but it does seem to smell more often than not when it happens. That along with the previous comments about the evap system makes me think this might be the cause. Do any of you get a gas smell as well?

Black 08 Z85 Colorado crew cab 3.7l, 3.73s, G80
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post #27 of 28 (permalink) Old 03-08-2017, 08:53 PM
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Update on my replacement of the Vent Canister Solenoid. I still have the Rough Idle at Cold Start. So, we can check that one off the list.

Still in search of...
Regards..
Mike
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post #28 of 28 (permalink) Old 03-14-2017, 04:31 PM
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Good info, but I do want to back up a moment here for some clarification.

I do not have a intermittent rough idle problem during cold or hot starts.

The rough idle only shows up when semi-warm. For example, drive until warm, park, restart truck after 1-3 hours. Rough idle will always happen within that 1-3 hour window. Outside that window, truck starts fine every single time.

I did have a stored P0300 show up yesterday, no CEL. Just scanned it and got a flag. No strong gas smell to report here, either.

Across most forum posts, P0300 is a sign of the dreaded valve guide issue. Turns out there are still a bunch of 07 and 08 I5's with this problem, but not enough to warrant a recall.

I checked which cylinders were misfiring and its 1 and 5, 9 counts over 200+ miles. 2-4 have zero misfires. It is going to get a compression check done this weekend so I can hopefully narrow down where the problem is. Really hoping the compression checks out... Would be an expensive fix for sure

Last edited by Zexy Magician; 03-14-2017 at 04:34 PM.
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