I have a 1992 230TE I have poor acceleration and on hills the speed drops off to around 40MPH. I have read the DIY section and have replaced the Over voltage relay, with no effect (I am getting voltage at the idle valve conectors). One very important thing is that the Idle valve has been disconected from the power cables. When you reconnect it, the car will start but will immediatly stall. I have talked to my local Mercedes Garage but they talk of checking the fuel pressure etc and ignore the fact that the idle valve has been diconected. I have replaced the fuel filter a couple of months ago. I think it must be an electical problem somewhere.

i think the shop you mentioned has a valid point in checking fuel pressure, since the engine has the problem when it is off idle, and at certain times under heavy load. it does sound like a pressure related issue.
as for them ignoring the idle valve they may not feel that is the problem but it should be diagnosed.
if it was at my shop i would recommend checking lambda and see where it is set or even if it is working, due to the idle problen it may be inop.
fuel pressure pressure tests and fuel volume tests would at least eliminate the pumps as a source of the malfunction or identify a problem there. as for the pump tests they can also look at the pump waveform and measure how many amps they are drawing.
Ray
mercedessd@cox.net

Thank you for the quick reply, I can see where they are coming from now.

After 3 days in the Mecedes garage, and a lot of pennies later, the problem was found to be that the Catalytic converter had broken up, blocking the outlet of the exhaust. New cat to be fitted, but the car is worth it.