I just wanna know if you guys always put premium gasoline(93 octane) on your MB cars.I tried putting regular gas and the not so rough idle on my car was gone,should i continue using regular gas.Which is better premium or regular?.

Ron

Premium only...both my gas engine Benzes have been euros with somewhat higher compression, but even if they weren't, the few cents you save is not worth the loss of the improved additive packages and available octane. It's all part of owning a high-end automobile.

Yep, 93 all the way!

Higher compression ratio dictates a higher octane. You could run lower, but that will reduce your mileage.

I always use Premium fuel, it's 92 Octane out here.
I would suggest posting a question why your car idles smoother with a lower octane in the TECH Forum. I am sure they can help you resolve the problem! Good luck!

__________________
2006 E350 w/ 155k miles (Daily Driver)

Previous:
1993 300E 3.2L Sedan w/ close to about 300k miles
2003 E500 Brilliant Silver (Had 217k miles when totalled!)
1989 300E with 289,000 miles (had for <1 yr while in HI)
03 CLK 500 cabrio (Mom's)
2006 C230k (Dad's)
1999 S420 (Mom's/Dad's)
2000 C230k Sport sedans
2001 CLK320 Cabrio (Mom's)
1995 C280 My First Mercedes-Benz... (155k miles. EXCEPTIONAL AUTOMOBILE. Was Very hard to let go of!)

the owner's manual says to use at least 91-octane fuel (this is for an M103 engine).

Never mind the effects on mileage - using a lower than 91-octane gas will drastically reduce the life of your engine.