my 1989 had a cold start valve that had been rendered superfluous when the dealer replaced the ECU back in 1993. Like you, I worried about it leaking into the intake manifold--I was having an issue with rich running on startup.

Eventually, I found the safest solution was to replace the entire fuel rail with one from a 1993 or later 240/940 where the cold start valve plumbing was already eliminated. I was never able to locate a fitting which would securely block off the flare-fitting port on the original rail. Do note that the clips that hold the injectors on changed around the same time, so be sure the new rail comes with the newer style clips.

John
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1989 245 245K / 1993 945 131K