The title says it all. I've had this problem for a while - idle is uneven - engine is shaking a bit, it almost feels like it's missing, at certain throttle positions the car hesitates when accelerating, and - at least I feel - the car should be quicker. A friend owning a w124 E36 says the same.
The car in question is a 1993 500E, 171k miles.
What I have done:
Replaced S29/3 Idle switch at accelerator pedal (Mercedes)
Replaced S16/1 Neutral Safety Switch (Mercedes)
Replaced Brake Lamp Switch (Mercedes)
Replaced vacuum seals between lower and upper intake (Mercedes)
Replaced rubber between ETA and MAF (Mercedes)
Replaced a few vacuum hoses here and there, checked the entire vacuum system in the engine compartment
Replaced gasket between intake and ETA (Mercedes)
Replaced intake gaskets (Mercedes)
Replaced distributor rotors (Bosch)
Replaced distributor caps (Bosch)
Replaced spark plugs (Mercedes) - they are the correct for the car
Replaced spark plug wires and coil wires (Bosch)
Replaced the oxygen sensor (Mercedes)
Replaced air filters (Mercedes)
I checked the MAF with STAR C3: Values are 1,50V and 21,8 kg/h at idle. Voltage rose to 2,0-2,1 at 3000 rpm.
I have checked the fuel pressure; it's 3,65 bar with vacuum @ idle, rising for a second if I press the accelerator and then going back to about 3,65 bar (with vacuum).
After shutting the engine off it stays at 3,65 bar for at least one hour (that's when I disconnected the metering device).
What I have not done/ought to be investigated:
Replaced the dust shields in the distributors - I have ordered them, but they have yet to arrive - could they cause this?
I have some funny noises coming from the catalytic converters - could they be blocked?
The car had been run with oily air filters, so the MAF was quite dirty. Could it be faulty - or how do the values look? I couldn't find anything in WIS.
As far as I know I don't have any fault codes now.
What else haven't I checked? Where do I go from here?