looks like a 1985 engine. That was added that specific year, there are slight differences in the CA cars. I believe that blue vac line modulates the turbo outlet. Also the 1985 diesels have an EGR "computer" (well, its an analog module) that feeds some of the emissions stuff as well as driving the tach on the clock in the instrument cluster. That makes for a smoother shifting transmission too.
I never set down to understand how it all operates but its there and the car usually drives fine without it! I believe its fail safe, ie. nothing is prevented from operating properly and causing the car to be inoperative. Very unusual compared to today's electronic nightmares!

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!