So...mid-last week, upon cold startup (sitting in parking lot at work all day - temps in 20's or 30's if I remember right) - the engine was running rough. I could hear audible miss'. On the drive - even after full warm-up - I noticed 2 things: 1) it felt down on power needing downshifts for 'normal' acceleration. 2) strange rpm bounce. Low-speed coasting, I would catch the tach bounce off of @500rpm (or there-about) and return to 'normal'. This would occur when doing about 30-40mph and I would take my foot off of the accelerator.

Only thing I did over the weekend was fill-up the tank. In addition - under the guise that maybe I had some bad gas (no beano jokes please!) - I added a bottle of Gumout 'complete fuel system cleaner'. I normally do not use those things, but figured what the heck.

OK - so after 2 days of driving it - the situation seems to be completely gone. I DID hear a miss on cold start this evening. But engine response has returned to normal - and the strange rpm drop upon 'coasting' has vanished. Last week that was easily repeatable - tonight...not at all.

So my question is - What the heck? Any thoughts?

Note - no codes where thrown - no CEL - no nuttin!

 

Did you go to a small mom-n-pop gas station that doesn't turnover a lot of gas, could have been gas that has been around awhile or moisture in the tank.

 

Generally - no. I generally fill-up at the local QT, Sams, or Costco. Turnover is not a problem. Having said that - I was thinking the same - hence the Gumout.

The RPM drop/bounce was a more curious side-effect of whatever the issue was - more-so than anything else.

Time will tell if it goes away and stays away.

 

Could have been fuel related. Also, no light doesn't necessarily mean no code. Check with a code reader for stored or pending codes to be certain.

 

This happened to me once- car was running rough for about 10 mins. I stopped and reset the ECU...Never repeated again in 3 years... Still don't know what happened. I had just "topped off" at a gas station.

 

sure you didnt pop 87 instead 91??

 

Yup - I should have specified - checked for codes w/OBD reader & Torque.

Hasn't repeated itself yet...

 

Actually use 93. But...even if it was 87, I would never expect that situation...

 

I'm experiencing this same issue. The car is rough and loud in cold weather, but the problem will clear up after driving 5 to 6 miles. The colder the rougher and louder. Definitely seems to be directly related to cold weather. The loud and rough is way more than the normal loudness of this car. Sometimes I get a smell of burning plastic right before things start to smooth out. The smell is not noticeable under the hood. Initially thought it was an exhaust problem, but the problem seems to be something that affects exhaust harmonics vs. a leak. Thought it cold be bad gas, but I use nothing but top tier brands and the issue has remained for several tankfuls. Any thoughts?

 

Using top tier gas does not mean you couldn't get a bad tankful...

I can't explain the smell of burning plastic - I can say that I smelled a significant amount of unburned gas when my situation persisted.

Could always try a fuel system cleaner (Gumout), etc - see if they have any effect.

Let us know - thanks

 

Thanks. I'm hoping that if it's gas it will sort itself out. I may reset the ECU just to see if it will help. Will post an update when I know more.