The warm up compennsator is not the cold start valve. Tthe W/U comp is on the right front of the intake manifold with two fuel lines running to it; the cold start valve is on the left front. The w/u comp has more than one function, despite it's name. It also regulates conntrol pressure, hence the clogged inlet filter fixing my problem. The system pressure regulator is on the upper rear (firewall side) of the fuel distrbutor (the thing with all the fuel lines coming out of it). The system regulator looks like a big nut when screwed in. The regulator kit (the part number for mine is 001 586 19 07) comes with a new valve and the rubber seals, and might be the culprit if you're losing fuel pressure while the car sits. The fact that it starts cold may be because the cold start valve is doing it's job or it might point to the w/u comp inlet screen being clogged. The check valve screws into the outlet side of the fuel pump at the rear of the car, under the fuel tank. You should have 5.0-5.6 bar system pressure and 3.4-3.8 control pressure when engine is warm.If you're pretty good with cars and are serious about working on that model, I strongly recommend the CD service manual from Mercedes. It is an excellent, very complete manual.

__________________
1983 380SL
1995 C280
1995 S500 coupe
1990 Mazda Miata
2004 Suzuki Hayabusa