I am working on a 1985 380SL with 80K that was off the road for 2 1/2 years. The car is now running reasonably well, but is not without its problems.

- With a rebuilt warm-up regulator, control pressure is to spec (1.9 at 70 degrees, and 3.4 warmed up, but the car stumbles on acceleration when cold. CP drops momentarily when engine vacuum changes as in a blip of the throttle. Both connections at the base of the WUR hold vacuum.

- I was able to set the on-off ratio to a nice fluctuating value anywhere between 35% and 55% at hot idle. However, when I hooked the CO meter up at the tailpipe, I observed that I could make a tiny adjustment to the mixture and watch the on-off ratio change AND watch the CO reading change. Example, on-off ratio at 40-42, CO at .5%, go a tiny bit lean on the mixture screw, on-off goes up to 45-47, CO goes down to .3. Go a bit richer and the readings move in the opposite directions. This was very consistent - both readings would move in proportion to the amount I turned the mixture screw. And I did wait for the readings to settle down after I changed the mixture.

My understanding is that when the engine is in closed loop, turning the mixture screw slightly should change the on-off ratio, but the CO should stay constant as the changing ratio means that the system is reacting and adjusting to keep the oxygen sensor voltage constant.

Putting both of these issues together, it seems to me that the fuel distributor is not respsonding very well, if at all to changes in control pressure from the WUR or the frequency valve.

Any ideas on how to test this, or other explanations for this behavior.

Other obeservations/data.

The frequency valve is buzzing
Starts easily, warm-up idle and warm idle very smooth.
Drives well when warm.
Oxygen sensor is new
Rebuilt WUR
Rebuilt idle relay
New fuel pump
New copper plugs

__________________
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