Hi all,

I have an '84 300sd that definitely has a vacuum issue. So far, I have measured vacuum at the pump, which was within the acceptable range, and replaced the little plastic fingers for the valves in the black plastic box on the valvecover. My symptoms are:

Somewhat harsh shifting, even with the shift modulator backed off all the way

Center dash vents do not seem to open

When I unlock the driver's door, the others unlock one by one, all within 1-2sec.

The engine takes a moment (less than 1 sec) to shut down after keyed off.

This all makes me think I have a leak somewhere. I have spent a lot of time with vacuum line diagrams trying to figure it out, but haven't found anything yet. Can anyone point me in the right direction based on these symptoms?

Thank you,
Jack

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Jack
1984 300SD. 115k miles.

The door locks have their own system. Isolate the "other consumers", meaning block off the HVAC system.

Does the engine shut off quickly?

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83 SD

84 CD

T into the vacuum line going to the transmission modulator and monitor the readings as you drive at various accelerator positions and then report back.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Generally, the problem is within these valves. Most folks have bypassed these valves completely as they only affect the EGR function on the '84 SD.

Do a search on my name for the full writeup on how to remove each individual line to the black box and eliminate them.