Took car in for routine maintenance and rough idle. Service is done and a diagnosis of ?bad VANOS? is made. After waiting 3 days for parts, car is fixed but rough idle continues. Two days later, on a Sunday, car won?t start and I could not jump it using my other car. Next day, BMW roadside assistance is called and after about 10 tries engin cranks, car starts and back to dealership I go. Car is kept for 2 days, no problem is found and everything checks out, I am told.
?May be you forgot to turn something off? says the SA. ?Like what?? I respond, ?Isn?t the car supposed to go to sleep?? ?Yah, you are right? is his answer.

What about the rough idle? It?s the Gas, says he ?The 93 octane has 15% ethanol and the engine software is not optimized for this mixture, new software will be coming out soon?.
As for a solution, ?try 89 octane gas?.
End of story.

 

So, did you get a good result by dropping to 89 octane?

We are discussion this same issue here - I suspect high-ethanol content too.

 

Another SA trying to BS a customer.
It's good to have a forum like this in these days.

 

BS ALERT!!!!!!!!!!!!!!!

 

Ethanol use in VA fuel is 10% (not 15%). The move to ethanol was done to replace the more toxic MTBE that was used before. BMW has stated that up to 10% ethanol is okay. Check your owners manual. The only thing that will happen by going to 89 (R+M)/2 octane is that the engine will retard detination and you'll have lower power output.

 

What you saying does make sense, but my personal experience with my 550 makes me want to try 89 octane gas. My car is now 1.5 month old and has around 1,500 miles. When I start the car in the morning the idle is somewhat rough and unstable and at first several stop lights the car sometimes shakes as if it is a subject to a strong wind. When I just got the car the engine was perfectly smooth at idle and on the move. The car (as all new cars) came with a full tank of gas. Ten days later the original gas was gone and after a fill up with 93 octane (Exxon) I immediately noticed that the engine was not as smooth as it was originally. Couple of days later I noticed rougher idle. At that time I blamed the gas station (bad gas) or the dealer filling the tank with some kind of high octane gas (very unlikely). But after I read the above message it seems possible that knowingly or unknowingly my dealer filled the tank with a lower octane (cheaper) gas. With all that said I will try 89 octane gas next time just out of curiosity.

 

I think we have summer formulated gas in certain states and that has been known to cause drivability problems. Of course I could have that confused with the Winter formulated gas... anyone?

 

BMW is one of four auto makers behind the "top tier" gas program which is intended to set enhanced quality standards for fuel that exceed the general requirements. These standards include the amount and type of detergent - but also the ethanol content that should be present. Top tier gas would include most of the premium formulations (Shell V-Power, Chevron Techron etc).

http://www.toptiergas.com/deposit_control.html

 

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