hesitation, loss of power when cold
 

I am not sure how to really describe this. When the engine is cold it stumbles, or misfires. It feels like the ac compressor kicks in or like tapping on the brakes while driving. It is most noticeable around 50mph and 2200rpm. Once the engine is warm it goes away. Any ideas what is causing this?

This is a 95 E300D btw.

Do a search for "surge," "surging," or "hesitation" along with "OM606," "E300," or "E300D." See if the symptoms described there match yours.

"Misfiring" is probably not the right word. Although you describe the engine as cold, by the time you're at 50 mph and 2200 rpm, all cylinders should be hot enough to achieve combustion even if you have a bad glow plug at startup (which would cause a brief rough idle/smoke). And, of course, there's no spark plug to not fire or fire at the wrong time. It's more likely that what you're feeling is a momentary loss of power caused by the air intake system or fuel injection system.

What surprises me is that your problem goes away when the engine is "warm." I assume you mean normal operating temp, i.e., 80-90 C.

Oh, another question: When you experience this problem, is it accompanied by any unusual noises? Bursts of grey/black smoke from the tailpipe?

I understand misfire is not the best term to use since there is no ignition system. The diesel terms are new to me.

Your description of momentary loss of power describes what is going on. The loss is for a fraction of a second, power is regained, ad then lost again. This only happens at a constant speed. Under acceleration there is no problem.

Warm = 60-80C

No smoke or noise. I say a puff of white smoke at start up once but that is it.

Ha! Welcome to 95E300D's. Mine does NOT like the new fuel apprently, and might have a bad prechamber, or two. While never being a proponent of fuel additives, you might just try some Howes Meaner Cleaner adding some lubricity and helping atomization with a bad prechamber. A band aid, tobe sure, but....

btw, have the fuel filters been changed out?

A bad prechamber does not sound good. Sorry for the newb question, but is it possible to repair those?

The new fuel being lower sulfur fuels? I live in a very small town but have many options for fuel since there is a lot agriculture. Maybe I should try a different source?

The spin on has been changed...waiting for o-ring for pre-filter.

Along with the search terms PJC mentioned, add "resonance flaps" to the list.

They can cause the symptoms you describe when gummed up or malfunctioning.

Did the search and I think it would be worth taking a look at that flap. Is cleaning it as simple as removing it and cleaning it up with carb cleaner?

Yes and no. Carb cleaner will work, but you really should clean the entire resonance tube/intake manifold, not just the flaps. And that's a very messy job. I know from experience. If possible, I'd recommend having an engine shop steam clean the parts . . . it will be worth the price.

BTW, make sure the electrical connector on top of the EGR valve is properly attached, with no broken wires. A broken wire there can cause this problem too, although logically it would not be limited to a cool engine.

Also check the electrical connections and vacuum lines to the flaps.