Yeah the lambda tower is the base adjustment for idle! Once the gas is pressed and the AFM plate moves down more then the EHA takes over! The EHA also is what makes the Duty Cycle change. For better fuel exonomy you can turn the EHA screw 1/8-1/4 turn Counter Clockwise and then it will lean the whole mixture out as far as I can tell. This would of course also make for a slightly leaner condition at WOT as well from what I understand on how the EHA works. As for Emmissions testing, since that is done at idle in most cases then the Lambda stightly lean would be good as well to correct that. Since if you notice the mixture will en-richen or lean based on the Lambda tower setting. Remember this is the base point for mixture so it will slightly affect the mixture throughout the whole range since the EHA can only do so much.

Edit: If you really want better economy and all then I would go with an EFI setup on there. This gives you much better control and you can setup the Fuel maps however you would like. There was a guy on 190revolution.net forums that was selling the kits complete and with instructions for around $1000 and he even had base maps for the M102 and M103 depending on what you order programmed in. He has a few kits left I believe. Also he has done many of these kits and put a lot of time in them, he is in Europe somewhere and has a shop that deals with EFI and MB and BMW!

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~Jamie
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2003 Pewter C230K SC C1, C4, C5, C7, heated seats, CD Changer, and 6 Speed. ContiExtremes on the C7's.

1986 190E 2.3 Black, Auto, Mods to come soon.....