My dad says he is getting an octane knock ever since he had the 15k service done on his 2002 300m.

He isnt sure if my mom might have put 87 gas in instead of 89... but to my understanding that shouldnt matter since 89 is "recommended"... not required.

Any idea what would cause this? He says when he puts his foot on the gas, he feels a click click click sound like its not getting enough power.

Could be a bad tank of gas.

The chance of bad gas increases during and after a rain.

dj, in PA ther switch to the winter blended gas at this time of year, it robs power, economy and generally makes the car run like hell, do they do that in the NY area? if they do it may be that as well

Ive never heard of that... something to think about.

Im gonna ask my dad this week if he ever brought it into the dealer or if it stopped.