Does it matter what octane to use in an A4 engine? I'm looking for best gas mileage.

 

87 is what it was designed for. Any higher and you may even see a decrease in mileage.

 

Thanks for the reply. Can the ECU be programmed to get better mileage and more power like some other vehicles? If so, is it worth it?

 

I don't really think so. most of those ECU reprogramming deals are kind of scams anyway. there is no real way to increase horsepower AND get better gas mileage. That is kind of a contradiction.
Since your ecu is OBDI though, you have more options than folks like myself (I have OBDII). I have heard Hondata is the best, but it is expensive (around $500)

 

Run gas withought ethanol...My neighbor is a chrysler tech, told me a guy at his work put acetone in his tank, something they used to do a long time ago, and gained 3-4MPG, he said like 2oz for every 10gal or something like that...i havent tried that, dont know what itd do to injectors or rest of fuel system...would have to look into further before trying...

 

acetone is a solvent that will eat away rubber seals or eat away anything non-metal for that matter. not a good thing. but yeah its getting harder and harder to find gas stations that arent using some type of ethanol mix. and it is true, ethanol will decrease your gas mileage no matter what tricks you do.