I love Seafoam.

http://www.youtube.com/watch?v=vRAV5ln5cUc

And as sptt says, check the duty cycle. If your air/fuel is off you will have a rough idle and probably bad economy. I used a simple digital volt meter to check and adjust mine.

M117 how to test lambda?

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car