Very rough idle in park...

[07TrailyLS]

I think I know what may be wrong but would like some advise. For the last 2 months, my idle in park and in drive at 0 is terrible. When I do a cold start I can see the exhaust sputtering for the first 10-15 seconds (pretty much choking). I just changed the plugs hoping to correct the issue. All 6 wore well (just turned 96k) except cylinder 5 had a small amount of oil around the threads. This has nothing to do with the idling issue so I'll move on. While re doing the plugs I pulled the TB and cleaned her up real good. Pretty dirty for only being a year since I cleaned it. Idle issue in park and at 0 in drive still persists. After watching a few videos on YouTube I'm falling into replacing the cam, and crank sensor, and the cpas. I've been shooting in the dark as this truck absolutely will not pull any sort of engine code. How the pcm is thinking its idling correctly is beyond me. Any opinions that could point me in a different direction or assuring me I'm spot on would be great Although I have a feeling that replacing one of these three will fix my problem. Thanks for reading guys

 

[christo829]

When mine started doing that, it was an indication that the motor mounts had started to turn in to rocks. It was really noticeable when it got cold. I've only got a little over 118k mi. No codes, but I'd often get a small CEL blip when coming off hard acceleration. The PCM showed nothing even in freeze frame or pending. I cleaned the throttle body, replaced the camshaft sensor and CPAS, but neither made a difference. I did not change the crank sensor. So far, everything has smoothed out properly. Hopefully it will stay that way as it gets cooler...

Good Luck!

Chris

 

[Mooseman]

The mounts are a good direction to follow. And to confirm, you did disconnect the battery or pull the PCM fuses while cleaning the TB?

If there are no codes, I wouldn't even look at the cam or crank sensors or the CPAS.

 

[07TrailyLS]

Moose, I did not disconnect the battery after the procedure. I'll try it when I get home. I'm ruling my mounts out because I can hear the hesitation all the way through the truck from engine to exhaust pipe. The other morning was cold and when I started the truck, the clear smoke that came from the exhaust came out in spurts right along with the roughness of the idle. That's the reason I'm ruling this toward he motor and not the mounts. Almost like the motors choking for lack of better term. Also, is there a specified amount of time to disco the battery for? Thought I remember reading somewhere like 35 minutes does a complete pcm reset .. I could be wrong

 

[Mooseman]

30 minutes but close enough

 

[07TrailyLS]

 

[christo829]

When my mounts were solidifying, they'd transmit the engine vibration through the truck quite well, rather than insulating. It was bad enough to eventually cause a misfire, and on cold mornings I would see puffs of exhaust, though I wasn't really analyzing their relationship to the lousy idle. Mine was rough at start and at idle until it warmed up. In gear at a stop it got bad as well. In gear and rolling it settled down. Last winter it was pretty nasty until the engine warmed up, unless I was in the mood for a back massage from the shaking seat. It even growled a bit going over speed bumps and such, which it no longer does with the new mounts.

What might be happening is that the PCM sees somewhat "off" data from the sensors, caused by the vibrations not being buffered by the mounts. It tries to adjust to some degree, but since the vibrations aren't anything consistent, it really can't. It's still happening at higher rpm's, but it's less noticeable.

Do you have a way to look at real time data from your sensors, above just checking codes? Might help focus on a cause more directly.

Cheers-

Chris

 

[mrrsm]

Just for the Hell of It... Can you remove the Serpentine Belt and Start The Engine and observe the idle in Park and also when moved to the "Drive" position with your foot on the Brake...and see if things change? Not for too long... Mind you...and not if your Battery is in a Marginal Power Condition. The Battery should be put on a charger immediately afterwards if possible after re-installing the Serpentine Belt after a few minutes of doing this test. If nothing else... It will eliminate any questions about ALL of the Belt Driven Accessory Components, Bearings and Pulleys...

 

[Mounce]

Pretty much unheard of that an idle issue be related to the accessory drive on these trucks or any other for that matter.... Didn't complain of belt accessory issues and it's unrelated to his particular issue, try to stay on topic.



I replaced plugs and cpas and my rough idle upon cold start seems to have disappeared. Plugs first and still idled funny here and there, had gotten the cpas code a few times over the years so threw one at it and have had no issue since myself.

 

[07TrailyLS]

Thanks Mounce. I took the day and probably the rest of the week off of work so I went out this morning and unplugged the battery. Letting the pcm do a master reset and I'll go from there. I just can't see this being any other issue than a bad sensor. I just wish the damn thing would throw me a code!

 

[Sparky]

For the sensors n such, I'd start with the CPAS - at least pull it and see what it looks like. Any oil in the connector, replace it.

You can have cases where the idle is rough due to poor cam timing, but it is still a clean burn, and it isn't spark timing related, so as far as the PCM is concerned things are still OK. Slightly early opening of the exhaust valves at low engine speed can lose the tail end of the power stroke as some just pushes out the opening exhaust port instead of shoving the piston all the way down. Although engine momentum and other cylinders firing keeps it going, it will be a bit rough/sputtery at that lower RPM.

My Camaro has an aftermarket cam in it which makes it idle roughly partially due to this (also other reasons such as more aggressive valve lift, overlap, etc). So thinking of this and reading your description is what brings that all to mind.

 

[07TrailyLS]

I'm going to pull the vvt solenoid when I get home tonight and check for oil. Pcm reset did nothing. I'll keep y'all updated

 

[gmcman]

You didnt mention this, but do you have any codes. ... (Service Engine Soon lamp illuminated on dash)?

Just a hunch, If you do have a code....it almost sounds like a bad coil. Number 4, as counted from front to back, sits under the hood cowl and gets water drained onto coil sometimes resulting in moisture in plug well. This comes to mind as you say the exhaust is sputtering and has been a troubled coil for others in the past.


Edit, I just re-read your post, didn't see that you aren't pulling codes.


Do you have oil in the CPAS harness?

 

[07TrailyLS]

I'll update y'all in the morning. Long drive home from work and it's pitch black out.

 

[07TrailyLS]

Alright boys. Verdicts in. Went out there an hour ago and pulled the CPAS out. No oil in the connector but I purchased a new one anyway. Let you know Sunday when it comes in if the problem persists.

 

[Mooseman]

Got an OEM or ACDelco right? Dorman blows on these.

If you pulled the CPAS out,how did the screens look? All there? Clean?

 

[07TrailyLS]

I cancelled the order moose. I was able to use torque to find misfires. 3 misfires coming from cylinder six on startup. Switched 6 to 2 and now two is misfiring. Ordered a acdelco from rock auto. Will be here Sunday. Update you guys then. Have a good weekend boys. Edit
Moose the cpas was clean as could be. No missing screens and I could see through each slot

 

[gmcman]

Make sure the springs inside the coil boots are not broken or missing. Also double check for any moisture in the coil pack wire connector.

Just curious, did you replace plugs with AC 41-103? I know you had this problem prior but just checking, these motors are picky.

 

[07TrailyLS]

FWIW, I. Myself only use ac delco for all replacement parts unless it's something stupid like a external sensor. Plugs, coils, engine mounts, and so on is delco only