Severe hesitation in 1987 300E
I have a 1987 300E and am experiencing some engine problems. The car starts normally but idles rough and when the accelerator is pushed down at a normal rate, the rpm's drop and occasionally the engine will backfire. If the accelerator is let up somewhat, or pumped, the rpm's will increase. This occurs when the car is in neutral (i.e. no load) as well as when in gear. The severity of this condition varies with time. It started out as only a minor hesitation but now is to the point where the engine sometimes will not rev above about 2000 rpm.
The problem started a few weeks after the fuel pumps and fuel filter were replaced. Since then, we've replaced the spark plugs, the oxygen sensor, and have checked the ignition distributor and rotor. This work was all done in the shop, but the mechanic there was not able to get the engine running smoothly again. He suggested replacing the fuel distributor and fuel injectors, a very expensive proposition, but could not promise the car would run any better afterwards. The mechanic did check one fuel injector and found it to be working properly.
I suspect some dirt in the fuel lines/system somewhere and have been looking at the other posts on this website to try and get some ideas on how to attack that problem.
I'd greatly appreciate any help you can give me. I'm not a mechanic, so please explain things in layman's terms.