I have a slight high idle, 800 rpm, and sometimes a rough warm idle. I have changed the injectors(inlcuding the cold start), FD, wires, coil, plugs, idle controller. 3 plugs were dark. I'm thinking the dark plugs are getting too much fuel, or maybe not enough air.

Could the air distribution hose leading to the injectors be blocked or clogged? Any other ideas?

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1989 420 SEL