Have you checked your AC compressor? The compressor clutch could be dragging against the polybelt if it is seized up. I had a similar issue on a 190E. The AC compressor seized up and killed the engine whenever engaged and idle was down a few notches.
Also, you might want to take a look at the throttle valve, could be stuck due to dirt accumulation and need a cleaning.
81 300 SD grey/palomino 168K miles
84 190E 2.3 black/grey 64K miles (wrecked)
85 190E 2.3 maroon/palomino 92K miles
88 300E desert red/palomino 204k miles
(made to look like a '94-95)
92 400E desert taupe/creme beige 120K miles
(converted to 94-95 E420 looks)