We were having a debate about my 1991 300D running rough and all of you, as well as other suggested that it was the glow plugs. I did check the glow plugs, and they all were fine. It turns out that my multimeter had a near dead battery. I replaced the battery im the MM and found out that plug #4 was bad. I just changed it, and the car runs great.
Can you find it in your heart to forgive me for doubting you??

That one's good for a chuckle. I can relate to the supposed infallibility of "the meter" and to the ease with which time, and battery life, slips by. I've gotten in the habit of dating batteries with a Sharpie marker when installing them to try to dispell the sense that I'm constantly replacing them. The facts prove otherwise in most instances (excludes my daughter's Walkman). When the battery in my Fluke meter expired recently, I would have sworn I just put a new one in it within a year. It was actually a little over nine years. That was almost exactly the lifetime of the only other 9v battery I've installed in it in the 18 years I've owned it. It has a "low batt" indicator, which I've never seen. I guess I've been lucky just to find a blank readout when the battery was gone.

I work in a highly regulated industry where I often scoff at some of the things we have to do to support the validity of data we generate in testing. Your experience is a good example of why we do need to be rigorous.

CJ,

Consider yourself forgiven. I'm happy that everything worked itself out and the vehicle is running smoothly again.

'Twas nice to know that the simple, logical answer was right after all.
With meters, I was taught to first, always short out the 2 leads and adjust the meter - this was with the old analog Simpsons. Digital meters don't have this feature, but it is still a good idea as it checks the battery and the condition of the leads.

Thank you for your help and my car thanks you as well. For good measure, I treated her to a new pre-filter and new fuel filter. Thanks again.

As someone around here once told me "I love the smell of diesel in the morning, it smells like victory!"

I forgive you CJ! I had the same problem myself. Is #4 hard to get to? I had to take my intake maniford off to get to my #4 - agh! At least I got to clean out all the gunk put there from the dang ole EGR!