Might want to search the mbcoupes.com archive for the, "surge from hell" threads. My experience (and also a friend with his 380) has been that the replacement parts are often bad (primarily the valve, but also the idle controller), or mismatched--can't get away with substituting a different PN/rev controller for a given valve. A theory would be the valve is a poor design to begin with and "new old stock" sitting on the shelves tend to freeze up. Also, the vacuum hose below is such a large diameter and odd shape, even if there are no cracks, it can be hard to get a tight seal. Just a few thoughts--wouldn't eliminate what you already replaced as suspects. Cheers, Andrew.

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86 560SEC
85 500SEC Lorinser
83 300D Turbo
75 240D