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Some days ago it was running fine when cold starting. I filled up with gas Monday night and yesterday (Tuesday) morning this happens.

Video of what I'm talking about here: Car Trouble - YouTube

On a cold start (overnight at -6C in the garage, or after working all day) the engine runs extremely rough, with vibration and much noise. After several seconds (about when the engine would normally go from high idle to normal low idle) it smooths out to normal behavior.
While this roughness is happening:
  • If I put it in gear the engine slowly stalls (takes a few seconds of struggling).
  • If I add some throttle it sounds a bit worse and RPM does not substantially change.
If I turn off the car while this rough idle thing is happening and try to start it again it turns over for several seconds before finally firing up and continuing the rough idle for some seconds before smoothing out.

After it smoothes out there are no more symptoms of anything weird; car runs just fine, no abnormal noises on acceleration or idle. And if I restart the car it will be fine; until the car has been turned off for sufficiently long enough to be cold.

White steam when I pop the hood is from my breath; it's cold, about -6C.

No mods at all; this is the second winter for the car. Oil was changed about 1000km ago (same 5W30 semi-synth I run all year).

Anybody have a clue?
Thanks.
 

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Having Fun In Japan!
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I've had the same issues last winter. Only happened twice though. I actually had smoke coming out of the exhaust when it happened but everything smoothed out within 10 seconds. Unfortunately there are no Hyundai dealers here in Japan and no one, except the expensive tuners, will touch the car because they are unfamiliar with the platform.
All I did after was take off the intake manifolds and valve covers and clean everything out. It's been fine since but winter is about here so I will be watching.
 

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Keeps Them Guessing!!
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What brand and grade of gas are you running? Do you always use the same station? It almost sounds like bad gas or water in the gas.
 

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I had the exact same thing happen to me recently. It happened on a really cold morning. Went to start the car, and it fired up, but really rough. The car was vibrating weird, and the sound was awful--almost like the cylinders were all firing way out of sync. Any ideas what's going on? I'm planning on taking it in.
 

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It doesn't look like anyone knows why this is happening for sure. It's happened to me a couple of times recently. 2010 3.8 GT with 36,000 miles on it. It has not done this in any previous years. It did it a couple of times one day about three weeks ago and then did it today. I'm in Atlanta, so I don't have the kind of cold being discussed above, but compared to normal here, these were cold mornings: cold enough to have frost on the windows.
 

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SloGEN
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Has anyone got any info in this? My 3.8 just started doing this last night after work, then again this morning. Also, from 65+mph, it'll jerk slighlty, like I'm tapping the brake when I'm not. That happened once before the engine issue, and seems to only happen when the engine's cold. I'm bone stock.

-Rachael

Eve -:{2010 Genesis Coupe 3.8 Track M/T in Bathhurst Black}:- :-D

Genny-:{2010 Genesis Coupe 2.0t Premium A/T in Bathhurst Black}:- *killed in her sleep* :(
 

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This hasnt happened to me in my Genesis, however in some of my older cars, the same exact issue ended up being a dirty/loose MAF sensor.

Can also try throwing a bottle of Chevron Techron im the fuel tank. That will clean out the system within a full tank of gas. Worth a try to narrow down what the issue is.


Sent from AutoGuide.com Free App
 

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Hmmm, I have an inclined driveway, and if I park with the nose pointed up, and if the gas is low (say 1/8th tank or less), and if there's been a weather change or rain overnight, then I can't even start it right off. It takes a couple of separate turnover attempts (which is embarrassing), and then it will finally start and sputter like the OP video, then it will clear up and you'd never know anything happened. I figure the rear fuel pump takes a minute to create enough pressure at the fuel rail when there's a lower than half tank on an incline, so, I try to give it a few seconds with the ignition on before I engage the starter.

Otherwise, I generally back in ;)
 

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Some days ago it was running fine when cold starting. I filled up with gas Monday night and yesterday (Tuesday) morning this happens.

Video of what I'm talking about here: Car Trouble - YouTube

On a cold start (overnight at -6C in the garage, or after working all day) the engine runs extremely rough, with vibration and much noise. After several seconds (about when the engine would normally go from high idle to normal low idle) it smooths out to normal behavior.
While this roughness is happening:
  • If I put it in gear the engine slowly stalls (takes a few seconds of struggling).
  • If I add some throttle it sounds a bit worse and RPM does not substantially change.
If I turn off the car while this rough idle thing is happening and try to start it again it turns over for several seconds before finally firing up and continuing the rough idle for some seconds before smoothing out.

After it smoothes out there are no more symptoms of anything weird; car runs just fine, no abnormal noises on acceleration or idle. And if I restart the car it will be fine; until the car has been turned off for sufficiently long enough to be cold.

White steam when I pop the hood is from my breath; it's cold, about -6C.

No mods at all; this is the second winter for the car. Oil was changed about 1000km ago (same 5W30 semi-synth I run all year).

Anybody have a clue?
Thanks.
I would check plugs and coils as well as MAF. Can you hear from which bank the sound comes from? If not, just replace all the plugs and see if it goes away since plugs are cheap. Or at least pull them to see if they look good or not.

If you can see a fouled plug, either hope that replacing it will make it better or consider changing the coil. That's where I would start. :)
 

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My 2010 3.8 ~30k miles did this exact same thing a couple months ago. Too bad I didnt find this thread sooner... I would have posted here instead of create my own thread. All I did was clean my MAF and TB. After cleaning them it still started rough a couple times but seemed to get better as the days went by. Probably after about 6 days of starting up weirdly it went away and never came back. I sort of doubt that cleaning the TB/MAF fixed this but was just a suggestion I got that sounded reasonable. Haven't done anything special like replacing head gaskets or sparkplugs. My gut tells me that moisture somehow got into the fuel system. I recall it was cool and rainy when this happened (rare for my area).
 

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2013 Sedan 3.8, less than 50k, rough idle on overnight cold start but only for 20 seconds! Then RPM increases to about 1400 and immediately smoothes right out and slowly drops to normal same as when brand new. With all I've read so far no one seems to have a clue. Cleaned TB and plate although not that dirty, no change. I believe it has to be something in the cold start circuit because it always takes the same amount of time and ALWAYS runs perfectly after initial 20 seconds. Help??????
 

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I am guessing, check how dirty the intake valves are.

If dirty, clean with some seafoam and a tooth brush.
 

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You can continue to question and still have the problem, or at least check the valves and possible fix your problem.

With 50k miles on a direct injected engine, I am positive that the valves have excess carbon buildup. If you clean them and it doesn't fix the problem, then at least you will regain your gas mileage back.
 

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So, let me get this straight, for a "rough idle that last's only 20 seconds on cold start and then totally smooths out" you think I should remove the heads and clean all the valves? By the way, my gas mileage is fine at 30mpg on hwy.
 
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