It seems evertime I change a filter, first the air filter then now the oil and oil filter the car runs rougher and now will not idle cold and sometimes warm too.
I used seafoam in crankcase before oil change, but I don't belive that cause the problem. I am also now, recently mixing a cocktail of Marvel Mistery oil, Iso Heat, Power Service (white bottle) with fuel fill-up. These are the only changes to the car.

Never use oil additives at any time.

Try putting the supply/return lines in a bottle of clean Diesel in the engine bay and see if that makes any difference.

There seems to be something missing in your thread. Is there anything else unusual you do before changing a filter out? Unlikely that changing an air filter would make a car quit at idle and warm temps afterwards in my opinion. Changing oil and oil filter likewise.

Could moving things around (particularly to remove the oil filter) have caused (or worsened) a vacuum leak? I know on my 300CD most of the vacuum lines exit the firewall close to the oil filter tower, and until recently everytime I even touched them one or more of the hard lines or check valves would pull out of the rubber Ts that MB used to connect them all together.

During my recent engine swap I cinched down a small black zip tie around each of the places where a hardline goes into a rubber T - to squeeze the opening in the T down to a smaller diameter and make them grip the hard lines more tightly. Seems to have worked. Moving them around doesn't make them come unplugged anymore, and my trans seems to be shifting more smoothly.

Just a thought...

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1984 300 Coupe TurboDiesel
Silver blue paint over navy blue interior
2nd owner & 2nd engine in an otherwise
99% original unmolested car
~210k miles on the clock

1986 Ford F250 4x4 Supercab
Charcoal & blue two tone paint over burgundy interior
Banks turbo, DRW, ZF-5 & SMF conversion
152k on the clock - actual mileage unknown

+1.. but first...

But first, replace both fuel filters. Maybe it is as simple as all your additives dissolving a bunch of crud, which has now washed into and plugged the fuel filters.

If that doesn't work, plumb a jug of fresh, clean diesel with no additives added in place of the feed line from the tank. Leave the return line as is so any additive-laden fuel can be flushed back into the tank. After the feed pump has pumped a quart or two of fresh diesel through the system, it should be flushed of any additive-laden diesel, and then you'll see what's what.

BTW, if the Heet you're talking about is the alcohol stuff, you may have harmed the injection pump -- I've heard water in the fuel is a fast way to ruin one, but never tried it myself. Alcohol-based Heet will help water mix into the fuel and thereby get into the IP.

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'83 300DTurbo http://badges.fuelly.com/images/smallsig-us/318559.png

Broadband: more lies faster.

I actally adjusted the idle, I think. That is if the adle adj. is the large slotted screw mounted on the fuel injector which adjusts the throddle linkage. I run better when warm now but still takes a long time to "warm -up" to idle. If my foot is taken off the pedal when cold the engine stalls immidiatly.

I used the Iso Heet in the red bottle that says its for use in diesel engines
Thanks for the info on the possible filter plug. I'll try that too.

Thanks, Speaking of vaccum leaks, after I shut off the engine and listen I hear a vaccum leak. I traced it down, through elimination of plugging off the tees, to the large black vacuum line going into the brake power booster. The leaking sound (with engine off) lasts for about a minute, then stops. Is there a possiblity that the booster is leaking?

That is your problem, the idle speed is too low. It needs to be 700-800rpm.

I voter for changing the fuel filter. Especially if not changed while car has been in your hands. Maintenance item anyways.