Rough Idle after short trip

[Datarock]

On my 17 Forte, I sometimes have to leave it outside the garage (due to friends/family coming over and blocking my entrance) and at night I put it back in the garage. The two times this has happened, the next morning, the car has a very rough idle that does not vanish for 4-6 minutes of driving. When I first turn it over, it's very rough and at each stop light/stop sign it continues. But after a few minutes of driving it vanishes and won't return unless I specifically have a very short drive, like from drive way to garage short.
What's causing this?

 

[Tones]

Running extra rich due to cold shutdown followed by cold startup. Most cars will do this.

 

[irad]

Clean your intake air control. I think it is dirty and when cold it does not let enough air into the engine. This is an easy fix but it could be something else. Just my best guess.

 

[AZjeff]

Originally Posted by Tones
Running extra rich due to cold shutdown followed by cold startup. Most cars will do this.


Can't agree with this. OP is in San Antonio, 40f lows isn't very cold to cause rough running. Does your 18 Subie run rough? Our 14 RAV never does.

 

[carviewsonic]

Under warranty? If it is I would let the dealer's service dept. take a look at it.

 

[hpb]

Originally Posted by Tones
Running extra rich due to cold shutdown followed by cold startup. Most cars will do this.


Correct.

 

[incognito_2u]

How many miles on the vehicle in question?

 

[Tones]

I haven't experienced this yet on the '18 Subaru, but have multiple times over the years in my Toyotas (Corolla, Avalon, Tundra) and my 8 cyl Ford F-150. If you are moving the car from one side of the driveway to the other and shut it down cold, it can run rough when you start it back up. Of course, we all try to avoid this (to avoid fuel dilution), but it happens.

 

[Datarock]

The car has 9,000 miles on it. It has only happened during those two instances when the car was turned on only for 15 feet of garage entry. Any other time, I have no issues and feel no roughness.

 

[dogememe]

What happens if you let it idle for a minute or two before/after you move it?

 

[mattd]

Take it to the dealer why waste time and money trying to fix it yourself when it's under warranty. They should even give you a loaner.

 

[hpb]

Originally Posted by dogememe
What happens if you let it idle for a minute or two before/after you move it?


This is the cure. Or rather than just moving it the few metres, go for a drive around the block. No point taking it to the dealer, there's nothing wrong with the car.

 

[HowAboutThis]

Originally Posted by AZjeff
Originally Posted by Tones
Running extra rich due to cold shutdown followed by cold startup. Most cars will do this.


Can't agree with this. OP is in San Antonio, 40f lows isn't very cold to cause rough running. Does your 18 Subie run rough? Our 14 RAV never does.


Cold start means cold engine. Engines run rich until engine temps are up. It's programmed into their computers. This has happened to me on every car I've driven. Nissans, Hondas, Toyotas, Subarus, Chevys,...

So, yes, fuel dump when engine is cold and a quick shutdown can mess with things. Once explained to me that the computer will be compensating as that's how it was shutdown, too. Makes sense. Don't worry about it, it's normal in any car. However, I always hate the quick start, move, shutoff on my cars. Makes me cringe...

 

[HowAboutThis]

Originally Posted by hpb
Originally Posted by dogememe
What happens if you let it idle for a minute or two before/after you move it?


This is the cure. Or rather than just moving it the few metres, go for a drive around the block. No point taking it to the dealer, there's nothing wrong with the car.


+1