Car has been experiencing rough start ups especially when car is cold. The "check engine" light comes on but after driving a couple of miles the light disappears and the roughness/hesitency resolves.

Took it to BMW and they found nothing wrong. However, they did advise me to use mid-grade gas only since there are not a lot of people buying premium because of the economy. This premium gas just sits at the gas station for ages and rots.
BMW also advised me against using Shell.

Any thoughts?

That's odd, I use Shell or 76 all the time here and they always give me the best fuel economy. I have noticed in all the cars I've had in Cali that Mobil, Chevron, Valero, and Arco consistently lose me about 2 MPG. That is why I stick to Shell and 76, best fuel economy and my car runs fine. Maybe it's a regional thing? L.A. people tend to baby their cars and put in the most they can afford so maybe there's a difference?

Doesn't make sense that people would buy premium, higher cost gas because of the downed economy??

But shoot, I pump mostly Shell since there are two by my house and on next to work.

It clearly states on the fuel cap to use only Premium (91+), I always use Shell 93 for the past 3 yrs.

I would tend to agree with the BMW dealer that in rural areas, the premium gas that is for sale might sit and rot (even when the economy isn't bad). Hell, even midgrade might be succeptable to this, because the majority of people don't care the type of gas they put in older cars, and buy whatever is cheapest.

However, in metro/urban areas I don't think is an issue. I use shell premium and have not had any issues. I don't think with the volume of cars we have in city areas any gas would just sit and rot.

I also don't understand if people are supposedly buying premium then how come it's sitting there rotting away??

It also says it in your owners manual, not recommended - it says "Premium Fuel ONLY". Maybe your dealer is just looking for a way not to have to cover future repairs?

crap...i always use shell v-power even when i drive to the boondocks. i purposely USE shell.

I think NYC530XI might be right in the sense that this is likely more of a rural problem.

I have been around for a few years and have been dealing with internal combustion engines all but perhaps six of those.

Never before have I heard the term "rot" when referring to engine fuel.

Can anyone who used the term above elaborate? Is there any more technical definition of rotted fuel? What might be the "shelf life" of engine fuel?

Thanks. I am just trying to learn.

sixcard :)