You will have a slightly rougher idle below 1.8% CO, this is normal. To get perfect idle you must be richer than that anyway.

I would check out the mixture control system -- you need to set the mixture with a duty cycle meter AND a mA meter at the EHA -- set the mixture to get 0 mA at the EHA (that is, no correction) and duty cycle near 50%.

If you have not done so, I would replace the O2 sensor -- if it's flaky, you won't get good mixture control at idle.

Another thing to check is injectors. If you have one dripping or not spraying well at low fuel delivery, the mixture will be wrong (leaking injector adds too much fuel, so the others are actually too lean).

Else live with the rough idle or higher CO.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!