Rough Idle After Sitting for 2 Weeks

[NaiveTurtle]

Hello all,

Ive tried google and here but nothing close to what I'm experiencing.

My car sat for a total of 3 weeks but was started briefly about 2 weeks ago. I just replaced my battery and started my S4 up to some extremely rough idling like a cylinder or two wasn't firing but there is no CEL present. It was about 50F outside if that matters. I immediately turned the car off and tried starting it again, this time with less rough idle. Seems to be idling fine once its up to temperature.

Does anyone have any idea? Like bad gas after sitting? Am i just freaking out for no reason?

[madkimchi]

i don't think gas goes bad in 3 weeks. i used to store my summer car for months at a time.

[MidwestB6]

I would say to let it idle for ten minutes or so to let it get warm, then drive it gently around the block a few times and see if anything out of the ordinary happens. Depending on your maintenance history, this could be a whole host of things. I'm thinking it's just cold if it's been taken care of.

[dparm]

Did you leave the gas tank very low? A bit of moisture could have built up. I think it's probably fine though.

[josh_avant]

I've had this happen to me twice now in the 6 or so months that I've owned my S4, both times the car was sitting for a week or two and both times scared the crap out of me. Both times the idle stayed a little rougher then normal for 5-10 minutes then everything seemed fine and she still runs just as strong as ever now. I searched quite a bit but have no real answers for what caused it, all I was able to find was a few discussions about coil packs, oil pressure and timing components, but I have brand new timing components and no other signs of coil pack issues so I don't think any of those would be overly helpful. Both times my tank was in the 1/4 to 1/2 full range, so dparm might be thinking in the right direction.

[NaiveTurtle]

There is just under 1/2 tank of gas in it. It started and ran just fine this morning. Hopefully this was a one time thing?

On a side note, Optima Red Top was a great idea, turns out the guy before me used some generic brand battery from O'Reilly Auto Parts.

[BITURBO Burg]

I just went through this about 2 weeks ago. The car sat for about 2 weeks with about 1/4 tank of gas. It was running terrible. Everything is perfect now, I think a lot of people have gone through this but no one has a definitive answer on why these cars do this.

[NaiveTurtle]

I am glad to see that I am not the only one experiencing this, it is even better to find out that it doesn't seem to cause any permanent issue with anyone else.

Thanks for the input everyone!

[Jake@JHM]

How is it running now, still bad?

[NaiveTurtle]

How is it running now, still bad?

Seemed to run just fine this morning, granted it barely got up to temperature before i got to the office. It started right up and did its normal idle at 1200rpm for like 15 seconds and then dropped down to 800rpm. Seemed to come up to temp just fine.

I really wonder if dparm is on to something. It has been raining a lot in the NW lately and the average temps have dropped probably 20 degrees. I wonder if there was some slight condensation build up in my gas?

[Jake@JHM]

That is very possible. Keep us updated if things start to run funky again .

[luvsspeed]

I had this issue if I really let it sit a long time and I have let my car sit for really long periods of time. Some time with a 1/4 or below or some times with a 1/2 take. I have always chalked it up to moisture in the fuel lines. I always ran fine after with no issues. I have a couple of other cars that do the same thing if I let them sit a few months or so. I have just always figured that its normal. Whenever that happens on anything I drive I just tap the throttle and clear out the line for that brief second. All is well after that.