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#3468612 - 08/29/14 04:27 PM Rough idle on cold start
Falcon_LS Offline


Registered: 10/03/08
Posts: 3881
Loc: Kuwait
Weird issue with my Envoy (4.2L L6) the last two days. On cold starts first thing in the morning, the engine idles rough (like a single cylinder misfire) for about a minute then returns to normal. If you rev the engine whilst it idles rough, it revs smooth as glass. No codes are stored in the PCM.

Worth noting, same thing happened this evening after the truck was sat for 12 hours and I had no cruise control. Pulled over, killed the ignition and fired her back up again and I had my cruise control back. Possible throttle body issue? Thanks!
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#3468614 - 08/29/14 04:31 PM Re: Rough idle on cold start [Re: Falcon_LS]
Skid Offline


Registered: 06/10/11
Posts: 388
Loc: USA - Southern California
If I had to guess, water temp sensor.

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#3468617 - 08/29/14 04:33 PM Re: Rough idle on cold start [Re: Falcon_LS]
Char Baby Offline


Registered: 05/25/05
Posts: 8750
Loc: Western NY
Possibly the throttle body needs to be cleaned or the(if this engine has one), the Idle Air Control Valve(IACV).

Research will help you fine where the IACV is!
Cleaning the T-Body with the proper cleaner may also aid in this idle issue.

Also, check for vacuum leaks!

This is just a start. Others will chime in with more helpfull information.

CB
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#3468623 - 08/29/14 04:40 PM Re: Rough idle on cold start [Re: Char Baby]
Bud_One Online   happy


Registered: 04/19/14
Posts: 1472
Loc: Spring,Texas
Originally Posted By: Char Baby
Possibly the throttle body needs to be cleaned


+1

Co-worker of mine has a 2004 Trailblazer with the 4.2 and had the same issue but never went away warm or cold. Throttle body was caked full of black goo. Cleaned it up and it ran great.
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#3468626 - 08/29/14 04:47 PM Re: Rough idle on cold start [Re: Falcon_LS]
Falcon_LS Offline


Registered: 10/03/08
Posts: 3881
Loc: Kuwait
Thanks for the input! The throttle body was cleaned roughly 3,000 miles ago and even then, barely needed any cleaning. It was almost spotless (engine's fed Euro V gas).

I monitor ECT constantly with my ScanGauge-II - at cold start ECT matches ambient temp and fluctuates between 190-195 F at operating temp - I guess that rules out the ECT sensor?
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#3468660 - 08/29/14 05:31 PM Re: Rough idle on cold start [Re: Falcon_LS]
Whimsey Offline


Registered: 12/22/02
Posts: 3559
Loc: The Garden State
Originally Posted By: Falcon_LS
Thanks for the input! The throttle body was cleaned roughly 3,000 miles ago and even then, barely needed any cleaning. It was almost spotless (engine's fed Euro V gas).

I monitor ECT constantly with my ScanGauge-II - at cold start ECT matches ambient temp and fluctuates between 190-195 F at operating temp - I guess that rules out the ECT sensor?

This may sound dumb but were they only looking at the throttle body on the visible outside of the throttle plate. My 1996 Ford Contour which burns no oil in 8500-9000 mile Oci's was clean on the visible front of the throttle body. Behind the throttle plate had black build up. After I cleaned it, it idles much better. Does it smooth up after it warms up? Mine now runs fairly stable idle, it only idles rough for a few seconds while still warming up, it only happens on the first stop after starting up. I'm sure my IAC valve should be cleaned but it's a PIA to get to so I'll live with less than perfect idle, but acceptable idle from a 4 cyl. I had no codes.

Whimsey

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#3468687 - 08/29/14 06:11 PM Re: Rough idle on cold start [Re: Falcon_LS]
Trav Offline


Registered: 11/20/06
Posts: 15127
Loc: MA, Mittelfranken.de
Originally Posted By: Falcon_LS
I monitor ECT constantly with my ScanGauge-II

Try unplugging that and see what happens. Start with the simple stuff.
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#3468717 - 08/29/14 06:51 PM Re: Rough idle on cold start [Re: Falcon_LS]
Merkava_4 Offline


Registered: 01/30/07
Posts: 15373
Loc: Clovis, CA
Originally Posted By: Falcon_LS
The throttle body was cleaned roughly 3,000 miles ago and even then, barely needed any cleaning. It was almost spotless (engine's fed Euro V gas).


Ah..........but are you just looking at it from the air side? I think you'll find that the throttle body looks quite different on the engine side. The engine side is what regurgitates all the combustion byproducts and oily PCV fumes onto the throttle body.

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#3468751 - 08/29/14 07:34 PM Re: Rough idle on cold start [Re: Bud_One]
01_celica_gt Offline


Registered: 07/29/13
Posts: 1764
Loc: St. Louis, MO
Originally Posted By: Bud_One
Originally Posted By: Char Baby
Possibly the throttle body needs to be cleaned


+1

Co-worker of mine has a 2004 Trailblazer with the 4.2 and had the same issue but never went away warm or cold. Throttle body was caked full of black goo. Cleaned it up and it ran great.


+1 just finished a 98 corolla with throttle body full of oil. Took off the throttle body and IACV, cleaned them both as they were both full of oil. Afterwards idle went from a constant 1400 to 750 rpm normal now. I did do an oil consumption fix, now I can barely hear the engine running and its revs REALLY smoothly.


Edited by 01_celica_gt (08/29/14 07:36 PM)
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#3468762 - 08/29/14 07:48 PM Re: Rough idle on cold start [Re: Falcon_LS]
Kuato Offline


Registered: 10/23/05
Posts: 5920
Loc: Colorado
How is your battery? If it's not in good shape it could cause a miss. I've had 2 different vehicles over the years that acted as yours does. Losing the cruise control was the tip off.
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#3468800 - 08/29/14 08:27 PM Re: Rough idle on cold start [Re: Falcon_LS]
toneydoc Offline


Registered: 12/16/11
Posts: 1498
Loc: War Eagle
Have you checked for any corrosion at the distributor cap and coils and spark plug connections. Have had rough running and misfiring in the past due to corrosion and buildup at some of the connectors on wiring.
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#3469019 - 08/30/14 06:39 AM Re: Rough idle on cold start [Re: toneydoc]
Falcon_LS Offline


Registered: 10/03/08
Posts: 3881
Loc: Kuwait
Found the culprit - we've been having some extremely humid weather of late and there was moisture in the coil in cylinder 1. Not sure how it got in, given I've generously applied dialectic grease when I did the plugs 25,000 miles ago, but I took this opportunity to pull the plugs out for inspection and reapply DG to all coil boots after blowing them clean with a compressed air gun.

That being said, I always clean my throttle body off the vehicle. In this case, it's drive by wire so I don't want to be messing with the plate. Removing it and generously spraying it with throttle body cleaner or brake cleaner does the trick, but it's always been clean with the gas I'm using.
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#3469050 - 08/30/14 07:50 AM Re: Rough idle on cold start [Re: Falcon_LS]
Char Baby Offline


Registered: 05/25/05
Posts: 8750
Loc: Western NY
Originally Posted By: Falcon_LS
Found the culprit - we've been having some extremely humid weather of late and there was moisture in the coil in cylinder 1. Not sure how it got in, given I've generously applied dialectic grease when I did the plugs 25,000 miles ago, but I took this opportunity to pull the plugs out for inspection and reapply DG to all coil boots after blowing them clean with a compressed air gun.

That being said, I always clean my throttle body off the vehicle. In this case, it's drive by wire so I don't want to be messing with the plate. Removing it and generously spraying it with throttle body cleaner or brake cleaner does the trick, but it's always been clean with the gas I'm using.


Well done!
Thanks for keeping us posted on the results!

smile
CB
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