Howdy,
I just purchased a 240D today. 1983, 218K miles, auto trans.
Car shifts hard and late, so I ordered the vacuum valves or switches today (the ones on top of valve cover are leaking). Have not yet fixed the vacuum problems.
Also noticed a slight howl between 45-55mph.
Took her for a drive this evening and almost didn't get home. After about 10 miles at 55-60 I felt something like surging for a few minutes, and then the car just started to fade and slow down. No change to oil pressure or engine temp, just slowed down to about 40. Pulled over and waited a few minutes and things were back to normal.
It happened two more times in the ten miles home.
Any ideas?
Trans fluid smells and looks good, though the level is 3/8" above the top mark on the stick with engine running.
Thanks. Good to be a Mercedes owner, I think!
Keith

 

Sounds like a fuel filter plugged or the strainer in the tank. The fuel filters easy to replace, so try that first. The strainer in the tank is a pain to do.
As far as your vacuum problem goes, clean out the oriface in the line between the vac. pump and the brake booster, the nipple that supplies vacuum to the valve on the side of the injection pump. It's an oriface and they have a tendency to clog with soot or oil.

 

I agree on the orifice, but you have already stated that the vacuum valves are leaking. How did you know that? Diagnostics or previous owner? The Howl could be almost anything on the car especially in a narrow rpm band. I'd change the differential lube and look for anything in the driveline that doesn't seem right. then work yuour way toward the engine. Definitely agree on changing the filters! The strainer in the fuel tank? Well? I had a similar problem on an Audi. Dropped the tank and vacuumed it out.
I have a 1983 240D that I just changed the tranmission in and have almost a 1000 miles on. Its been a reliable car so far.