I have the same '97 E 300 D, and my advice would be to start by doing only routine maintenance, fluids, filters, etc. You will likely have some diesel fuel leaks that will need to be fixed. The EGR is best fixed by feeding it filtered air and plugging the hole on the exhaust manifold. This will not set a CEL, and will cut down on smoke, and increase pep modestly. The car will tell you what needs to be done. If you listen to all of us about what should be done, you will soon decide that a preventive overhaul is in order. The car works well in flat country, but is less satisfactory in hilly country because of it's modest acceleration.

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'97 E 300 D