Well you have just screwed the pooch.

The mixture is only adjustable after you have over-riden all the electronic and lambda controls a good hiway drive and you won't have any catalyst left (maybe no floor).

The reason you have corrected the misfire with mixture is undoubtably due to a secondary ignition short circuit (usually plug wire ends). As soon as the mixtures drive required voltage above the shorted path voltage, you don't fire on that cylinder anymore. Leaner mixtures require higher firing voltages. The overall warm mixture is not adjustable! Only the base point is adjustable.

The normal correction of mixture even after component replacement is usually in the realm of 5 degrees of rotation not a half turn (180 degrees). Just add nitrous and you be running top fuel eliminator (bg).

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician