Re: 89 300E, tough please

IMHO the fuel pressure is probably OK because the problem only occurs at cold starts.

Fuel injected engines have a "cold start system" that injects additional fuel into the engine for a very short time during cold starts - five to fifteen seconds to help get them started and for initial warm-up.

Basically, there's an engine temperature sensor: ON below a certain temperature and OFF above it.
A relay that's ON longer as the temperature is lower.
And an electric cold start valve: ON injects fuel, OFF cuts off the fuel.

One of these isn't doing what it should be.