Diesel Diagnosis: Neighbors '84 190D runs weak...

1984 190D 115K runs weak when started sometimes, as if starved for fuel. After a few minutes wait, it may start and run normally. Once it starts normally, it continues to run normally until it is shut off. But upon re-start, it may be weak again.

He has changed all of the fuel filters, and the dealer says the fuel pump is ok. I thought maybe a malfunctioning fuel pump relay, or perhaps a faulty fuel stop valve. Neighbor says the dealer did not check these items.

Any suggestions?