Don't know about the oil pressure but the idle problems strike me as being caused by an air leak. Replace your lines and clean out your strainer. A plugged strainer could cause enough suction in your fuel lines to pull in air at a marginal connection. Strainer is easily accessed on the wagon. Drain the fuel by idling the car and running the return line into a fuel container until the engine stalls when the tank is empty.

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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