Chevron Techron Fuel Sys. Cleaner. You'll find it in black bottles with Chevron's logo on it. This stuff is strong, per the label "......use every 3,000 miles". So I gather that anything sooner that 3K would be harmful. I once used some fuel sys. cleaner from STP that said flat out, don't use any sooner than 4K miles.
Each bottle is good for up to 12 gallons. If your car is like our newly acquired SL, and has a fuel tank of 22 gal. Then you'll have put in 2 bottles. The lable also say to pour this stuff in before fiulling up. I guess this way it mixes real well.

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1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
MBCA member