Did you tried doing a fuel pressure check? It would tell you if car is holding up the pressre, if not, it could be Fuel accumulator, check valves, Fuel distributor etc. The reason you morning starts are ok, because cold start injector assist the engine by squirting gas in the engine at low engine temperatures. Once car ran and then sits for a while, on next start the CSI do not kicks in since engine temp. is not low engough.

Good luck

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87 420 SEL
Looking for a nice mid 80's MB diesel.
87 BMW 528e (Sold)
99 TOYOTA 4Runner
1989 Honda Accord (Sold)
1988 Honda Accord (Total)