I recently had the same problem with my '86 420SEL. It was 196 on the hydrocarbons (passed everything else no problem) against an allowable 102 (Ontario Canada). They adjusted the lambda (I think that means new 02 sensor) and that brought it down to 160. Then they did a motor vac and had me drive it really hard for a few days to clean it out. It tested the third time at 101 against 102. That was good enough for me. (also had new plugs put in). I have a bit of a rough idle (not related to secondary igintion as that is all brand new) that I think is one or two cylinders running rich due to worn injector plungers. Have Benzmac's suggestions checked out. Also it is a good idea to have your engine good and hot for these tests as that usually helps. I would sayu drive it for an hour on the highway and then have it tested immediately.
1995 E420 - retired
1986 420SEL - retired