2011 Chrevrolet Colorado vortec 2900 2.9L Intermittent rough idle

2011 Chrevrolet Colorado vortec 2900 2.9L Intermittent rough idle

This truck has been through it.

History: previous owner had the engine replace with a rebuilt. Truck runs extremely smooth. Then intermittently will run extremely rough at idle, after warm and driving for about 45 minutes with outside temps high. No miss codes. New owner had a mechanic look it over and ended up replacing timing chain and gears on the front. The back appeared new. New owner replaced VVT solenoid, cam and crank sensors. Mechanic states that it was getting a code for crankshaft and exhaust camshaft position coorelation , and that his snap-on tool wouldn't communicate or would communicate and then drop connection when trying to operate various functions. They took it go GM who told them that the techii communcated pefectly and that the truck ran fine with no codes. Transmission is "missing a couple gears", per the mechanic. They took it to a transmission shop who said the transmission needs replaced, but that it wouldn't fix the engine trouble. Mechanic decided to punt and bring it to me to look over the electrical.

Owner arrived with truck running very rough, and said it started that after driving a while, after hard braking. My techii communicates fine with full bidirectional on the ecm and tcm. My dumb scanner communicates perfectly also. There were several codes, including Bank 1 lean, cam/crank variation, and several codes for ecm communication. I went through the truck and checked all electrical connectors, found a few that were not clicked down. But nothing that caused the truck to run rough, or better either. Fuel trims were lean, and map sensor was intermittenly out of spec, and would improve with throttle. However, throttle was unable to be held steady at say 1500,2000 without jumping up and down. Eliminating evap at the throttle body fixed the fuel trims. Replaced MAP sensor, which improved the throttle issue and the MAP readings. System was smoked and found no other vacuum leaks. Throttle body cleaned (looked like it had already been done recently), but i went over it again.

Once I cleared the codes and after hours of running and driving, only the intermittent exhaust cam/crank coorelation code comes back. (P0017) I drove this truck when it was much cooler the other evening.... It drove amazing until I was over an hour into the drive and it just hiccuped once after slowing to enter a neighborhood. Then returned to normal idle. The next day I drove it in the heat, and it was back to about 45 minutes into the drive it started idling like it was "cammed". So much so that my neighbor up the street asked if it was cammed when I stopped to say hi bringing it back to the shop. If you throttle up above 1500rpm at idle it will go back to idling normal. You can cause the rough idle to return by driving, generally at a stop, but I've also gotten it to rough idle by sitting and randomly increasing/decreasing throttle. I can cutout injectors, and ignition, by cylinder, while it is in rough idle, and the truck responds as would be expected. All numbers look good EVEN when idling terrible.

I have gone over nearly the entire wiring harness, and there is nothing suspect. One very curious item is that the TCM gets very hot. In these temps everything is very hot. But it seems unusually hot after the drive. Next step is testing it out. Although they are pretty cheap, and cheaper than my time to put it on my bench and wire it up. So considering changing it (don't tell Paul). This being so intermittent, and seemingly not happening when cool, also make this more complicated to replicate on the bench. This truck has idled for HOURS with no problem. Driven, and will start acting up. I did notice, if I disconnect the TCM the idle fixes momentarily before the truck dies. Also, with the truck in rough idle, I can cool the TCM and ECM, and the problem remains until they are reset. If the truck is in rough idle, restarting always gets it back to smooth idle.

I am looking for any and all input! I've put way too much time into this truck for this customer already! Looking forward to hear all the wisdom from you GOATs. I'm sure I've left some things off that have been checked. But I've done the best I can to give you all an idea of what I'm dealing with. Anyone seen similar? Thoughts on the TCM failing?

Some ideas...

Look at the exhaust cam data when it's acting up. Actual vs. desired camshaft position. Perhaps the exhaust cam phaser isn't locking when returning to an idle when hot. That was never replaced, right? You can see South Main Auto's video about an older Colorado - the phaser had play in it.

Look up the description and operation of the TCM and also the ECM and engine controls. See how the TCM might affect engine operation.

What are the specifics of the no-comm code? Was it in the ECM saying no comm with the TCM? If so, then I'd say it looks like the TCM is indeed flaking out when hot.

Check the Mode 6 misfire data when it runs rough. See if it's certain cylinders.

Check spark and fuel timing when it's running rough.

When it's running rough, does spraying brake cleaner in the intake smooth it out?

Thanks Joshua!

I actually called the mechanic several days ago after seeing South Main Auto's video. And the mechanic verified he did change the phaser because he too had seen that video. LOL.

I know the TCM is in the comm loop with the ecm. So it appears, no TCM, means no ECM comms. And bad comms to TCM means no comms. I've not been able to get any communication codes to pop however the entire time I had the vehicle. They were only there when it arrived. And I'm thinking that had to do with someone disconnecting the TCM.

I don't recall the communication code. I normally write everything down or take pictures. But I assumed it would recur quickly. Not so much.

I checked mode 6 misfire, and there are zero misfires.......... yup. Zero. And when I cause misfires by cylinder, it's noticeably missing at that point on each cylinder.

As for spark/fuel timing...... I'll need to check that again. The spark advance, I believe, was all over the place between -5 and 17 when it was acting up. I need to make sure I'm not thinking of another reading. But I'm pretty sure that's right. I'll check it in a bit. I'll have to take it out for a drive to get it acting up again.

I haven't tried juicing it in the intake, just because I assumed it would smooth out, since tapping the gas smooths it out. Raise the RPMs and it will, generally but not always, start idling normal. Like something is unsticking or resetting or.... who knows.

Thanks again for the reply. I look forward to any help you and others can give!

Correction. The truck will run without the TCM installed. You can connect and disconnect it, the idle does momentarily change when it's being connected/disconnected. However, when it is rough idling, it will idle up and then die when you disconnect the TCM. May or may not mean anything. I've tested the tcm connector, and checked the tcm for shorts with nothing glaring.

It sounds like your most promising lead is the fact that it dies when disconnecting the TCM only when the problem is occurring. You need to find out the TCM's role.

Was the new phaser and solenoid OEM? They typically act out at idle when hot, and smooth out when you increase RPMs even just a little. But I do think your problem is electrical.

SD has shown before that some GM communication circuits are hard-wired inside the module so that there's still a loop even if a module is not communicating.

Adding fuel to the intake when it's running rough should be insightful.

Another thought...when it's idling rough, unplug the VVT solenoid(s) and give them a quick "blip" via jumper wires. See if that smooths it out. This is a tip from FordTechMakuLoco regarding Ford's 5.4L, but it may help here. If they do, the solenoid is stuck. Another possibility is the phaser is not locking into base timing. Perhaps restarting it locks it in.

I'm not sure if they were OEM parts replaced or not. But that was my exact concern. This really seemed like it might be faulty new parts, since it's acting like it's randomly out of sync.

That's some golden info there. I'll definitely give those a shot today.

You can also check oil pressure when it's running rough and see if it's above the minimum spec.

Does your scan tool have Camshaft degrees variation from expected?

Blipped the vvt, no change. For grins I unhooked the tcm while running rough again, since it always runs better then dies. Nope not this time. Just the last 5 times. Ugh. I have a tech2. So I have desired/angle/variance exhaust cmp. I am fairly certain it was on point when I checked it before. But I am trying to get it to run bad again to check. I have been staring at this one project for days. With just a few jobs in-between. So I’m starting to lose it. Lol. I’ll report back soon! Thanks again! I’m still pondering the water issue on the other thread. I’ll chime in over there in a bit.

Driving around the block a couple times triggered it. Desired/angle and variance are all at 0 while sitting here running like dog water. The variance did randomly hit 15 as this started acting up. Revving the engine desired/angle and variance stay at 0. Revved some more and they started responding again. Drove it around and all three responding and no hiccups. Variance went to 26 and it started up again. Same result, and all at 0 when revving. Driving gets it responding again.

That’s the ticket. Just not sure what the ticket gets me into, if you know what I mean.

Added note. It has happened in park once or twice. But not consistently at all. Driving or in gear with throttle and brake trigger it consistently. For what it’s worth.

It runs rough only when returned to an idle, right? Is it below a certain RPM?

You said, "Driving around the block a couple times triggered it." Does that mean the engine was cold?

Are you saying there is cam angle variance when it first starts running rough, but then the variance goes back to 0 even while it keeps running rough?

Did you blip the VVT solenoid while it was running rough?

FYI: you can get a cheap TCM programmed to your VIN on eBay for <$60.

JoshuaK wrote:

It runs rough only when returned to an idle, right? Is it below a certain RPM?

I felt it as start as soon as the variation spiked.

You said, "Driving around the block a couple times triggered it." Does that mean the engine was cold?
Sorry. No. The truck was warm and had been idling for probably 30 minutes. I was revving intermittently to try and trigger it without driving with no luck. Driving it triggered it.

Are you saying there is cam angle variance when it first starts running rough, but then the variance goes back to 0 even while it keeps running rough?
Yes. This is correct. Variance spikes while driving. When off throttle it returns to zero with rough idle. And all 3 readings stay at zero even when revving. But it eventually may or may not reset and start showing readings again without rough idle. Only to be triggered again by driving.

Did you blip the VVT solenoid while it was running rough?

I did. No change.

JoshuaK wrote:

FYI: you can get a cheap TCM programmed to your VIN on eBay for <$60.

I noticed that! Probably worth the money just to eliminate that.

If you apply power to the VVT solenoid while idling for just 2-3 seconds, it should run very rough or stall, and then immediately return back to normal idle when you remove power.

You should check the fuel trims while the variance is spiking, then keep looking at it when you idle it and it's running rough. One guess is that the variance (oil pressure, phaser, or solenoid problem) is causing the PCM to compensate with adding fuel, then when you idle it and the variance goes back to zero, it takes a while to get the air fuel ratio right.

I would say check oil pressure at hot idle when it acts up, and if that's good replace the VVT solenoid with OEM if it's quick to get to. If not quick to replace, then replace both solenoid and phaser with OEM.

JoshuaK wrote:

If you apply power to the VVT solenoid while idling for just 2-3 seconds, it should run very rough or stall, and then immediately return back to normal idle when you remove power.

You should check the fuel trims while the variance is spiking, then keep looking at it when you idle it and it's running rough. One guess is that the variance (oil pressure, phaser, or solenoid problem) is causing the PCM to compensate with adding fuel, then when you idle it and the variance goes back to zero, it takes a while to get the air fuel ratio right.

I checked the fuel trims when it was running rough when he first dropped it off....... and I checked it numerous times since.... because of course they should be all over the place or out of spec...... nope. Dead on even when running terrible! Which baffled me, since it seemed like it would have to be compensating for whatever was the cause of the issue. Crazy, right?

Owner just dropped a replacement TCM. So I'll be connecting it and programming it to the truck in the next hour. Really praying this fixes it.

I'll be praying!

It's in "closed loop" when you're looking at fuel trims, right?

I'm curious to know what equipment you're using to program the TCM. Are you just having to write the VIN # on it? is it a J2534 tool?