Erratic sluggish acceleration/rough idle

[bobirving]

I've got a 91 Mercedes 420SEL about 111,000 miles on it. Great car. For past few months, I've noticed idle at a stop (when in Drive) is very rough, feels like a plug is "missing", but not always rythmic. It's erratic. Same with acceleration. Weak, and erratic and jerky at first, then picks up. Not strong and smooth acceleration like normal. Driving me nuts!

I've checked vacuum lines (as much as I could, and am reasonably sure I don't have a problem there).

I'm in process of replacing spark plug wires and leads (plugs are 1 yr. old), and the distributor and rotor (also going to check timing, etc.).

Question: Does this car have a "knock sensor" (say, like Volvos, etc.?). When those go bad, it produces similar symptoms....

Any ideas??

Bob Irving
Charlotte, NC