When accelerating quickly (almost floored) my 85 300d has started to lose power every second or less and then put power on again above 3k rpm. Any ideas on what I should check first when I get home? Vacuum is fine in terms of shift quality. I am assuming turbo or fuel system related.

Interestingly when pretty cold out (50 degrees), and when the car was cold it did not exhibit this problem on my second trip today. As soon as it was warm it started up again. Thanks for the advice in advance. There is definitely a wealth of knowledge here.

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1985 300D
1985 Vanagon Westfalia
1980 Honda CB750k
1998 Honda Civic

I'd first want to rule out fuel fliters or a leak in the fuel system, as that's the most likely cause.

Is this happening with the A/C on? If so, if you roll the window down and try accelerating while next to a stationary object (like a concrete barrier on the interstate) can you hear a clicking sound? If so, check the A/C cut off switch on top of the valve cover (it's part of the KLIMA system that is on the w123s for '85 only). On my '85, the switch became intermittent with age and would cycle the compressor on and off under moderate to heavy acceleration, causing a surging feeling and making a clicking sound. It would get worse as the temperature under the hood increased (I guess causing the old plastic to swell).

Good luck.

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Christopher
'06 Mercedes E350 station wagon (silver/black)
'85 Mercedes 300D (black pearl/palomino)
'85 Mercedes 300SD (smoke silver/burgundy)
'79 Cadillac Sedan DeVille

'05 Toyota Camry (because always running is nice)

'85 Mercedes 300D sold back to orig. owner 8-1-06
'84 Volvo 264GL Diesel, owned 2000-2013