Doktor Bert, Danke for the great post, this has awakened my thoughts about the performance of my '85 engine (transplant into '79 300TD). I have been attempting to solve the high idle speed it has, it idles around 750 maybe a tad over that as read on the tach in the instrument cluster and the car creeps more than it should with the brakes off. I have been living with this for almost 2 years since the engine was rebuilt by shifting to N at stop lights. I have driven it cross country and it runs fine after it gets up, the turbo was also rebuilt and spools up (I read boost pressure in the cabin) but the acceleration seems to be lacking. I tweaked the ALDA two turns out and it gets up off the line but still I think its missing a little oomph, the torque curve seems a little steep or something, maybe that isn't the right description.

Everything topside is new with first oversize pistons. Rebuilt IP by Pacific FI and matched injectors.

After reading this thread, I now wonder if my timing might be retarded?
The engine starts perfectly with a twitch of the starter switch and has no nailing cold. If advancing the timing will reduce idle speed then I am for that, I have loosened the idle set screw completely out and never able to drop the speed below 750. The possibility is that IP was set up wrong, but I want to dismiss that because Gus is very thorough and I hope would not deliver something with a problem. I have seen the internal rack, and the rotating wedge that controls flow of fuel as the linkage is operated, its an amazing Bosch design that goes back some 50 years.

I am going to go after this issue as weather improves. I think a little effort will make the car run like my other wagon, a stock '85 with 220K miles on it, it has better acceleration than the rebuilt engine discussed above, even with the taller gears in the differential.
My herd:
1971 220 (gas) 4-spd manual 106441
1979 300TD w/ ’85 turbo engine 296650 (14K on rebuilt engine)
1983 300D 243280 w/2.88 differential
1985 300TD 223470
1987 300D 262300

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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!