This is a former Starmark car with 102k that has had a lot of work due to me whining about every last thing at the dealer. Past 4 tanks or so, various stations, all 93 octane, motor buzzes and vibrates, and my mileage is notably down.

Winter fuel?

I use techron every 5k, the car has had the entire plug/wire/resistor setup replaced 15-20k ago, oil is clean, motor mounts just passed indie inspection.

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former: 83 300D, 97 C230, 93 400E

current: 08 C300 Luxury , 92 500SL