What is your on-off ratio doing when you tweak the mixture? In theory, your small adjustments should cause the lambda system to compensate and the CO would stay constant.

It sounds like you may have an O2 sensor or other emissions component problem.

BTW, a 1.8% CO is high - you need 1.2% to pass in Virginia.

What vacuum reading are you getting at idle? If the idle is smooth, I would discount the claim that you need to seal the intake.

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe