Digging thru the archives, one sees many posts that attribute a hard cold start & high idle to a faulty OVP.

I realize yours is dual-fused and not that old, but....

Just for the heck of it, pull it off and shake it. Make sure the fuse flap is held down. If you hear anything rattling when you shake it, you have a bad OVP. There are theoretically other ways to test the circuits controlled by this gadget, but what I just described indicates a bad OVP.

It's simple to do and worth a shot.

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'91 300-SEL