A *great* MB mechanic and $500 resolved the problem. The computer wouldn't produce codes, though the CHECK ENGINE was coming on, and the power loss occured just after a hard deceleration.

Turns out the OVP relay malfunctioned during the
deceleration, and the engine idle wasn't being done properly. Also after turning off, then on the engine, the CHECK ENGINE came on for a minute.

Though the computer couldnt send out codes, it knew that the O2 sensor was bad (crudded up w/ 60K miles on it...definitely time to replace.) So, with OVP and O2 replaced, and Lambda adjusted, alles is gut ins MB-auto Deutschland!

Hey guys:

I fixed a very similar problem on my mother's 88 300E by replacing every rubber vacuum line I could find, and replacing the rubber hoses from the fuel distributor to the idle valve and idle valve to intake manifold.

All the rubber parts were either rock hard or melting, and all appeared to leak. The hoses on the idle valve were very hard and loose -- this will affect idle mixture considerably, depending on whether they were leaking or not.

A tune up (plugs, wires, rotor, cap) and a long trip and it runs beautifully!

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Just got back from my HONEST mechanic who usually takes care of my Honda accord, and does also work on my 300E. I had the oxygen sensor changed at 167,000 km by a SHADY Mercedes mechanic who claims to replace all parts by original Mercedes parts and today at 244,000 km have replaced the oxygen sensor again, and to my surprise the oxygen sensor taken out by my Honda mechanic is a FORD oxygen sensor which I paid 165.00 for. I would not have minded if this was told to me, and that he assured me that the part had the same qualities, and of course save me a few dollars. Now I know where a few rotten and stinky apples can ruin the reputation of other honest hard working mechanics. Just wanted to get this off my chest, because I feel cheated. If anyone wants to know the name of the shop I dealt with (IN LAVAL,CANADA). send me your E-MAIL and I will forward it to you. I might have been fished in, but I hope no one else gets hooked by this guy......WOW that felt good.

After my 300E's repair (O2 and OVP), the mech gave me the OVP to play with. Checking is easy. Look at the schematic on the side. Check the diode paths with an ohmmeter (low resistance forwards; backwards they are high ohms). Next check relay for *open* (roughly infinity ohms.) When I tore my old one open, and played 12V on the relay coil, the ohms through the relay contacts went from zero, to infinity, then zero to 1.5 megs (!!!), then zero then infinity. It is this 1.5 megs that caused the electronics problems. Relays sometimes get what I call whiskers across contacts (crud, microscopic metal, dirt, etc...) And no way to open/clean/reassemble this charmer! Just replace.