Run the Seafoam straight into the intake. Do this by dropping a vacuum hose in the can and letting it suck the cleaner straight into the engine undiluted with gasoline. You will have to manually play with the throttle to keep it running and it will smoke like hell. Then shut it off and let it sit overnight. Drop a second can in the gas tank (not the can, just the cleaner) and drive. If you don't get a good cleaning on the injectors, repeat the whole process in a week. Like Larry said run a higher octane for a tank or two, or try a can of octane booster.

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65 190d sold
85 380SE sold
87 560 SL 180K
84 380SE 96K (mint)