MCELROYB , AMG280,
I too have a 92 400E(188K mi) which exhibits a rough idle upon cold start up. Once the car warms it idle smoothly. I am NOT experiencing the problem exactly as AMG280 described(my acceleration at all speeds under all throttle positions is smooth albeit a bit stiffled) but the car continues to idle roughly despite having changed out the TBA , EGR, Plugs, Wires, Caps,(No Coils yet) Rotors,Most vacuum tubing and the Intake Manifold "O rings". It does not appear to have a vacuum leak but its really unnerving to see the car running so poorly. I'm hesitant to take it to the dealer for the reason you both mentioned...They put on a witch hunt to the tune of $85-$100 / Hr. Hell if i wanted an EXORCIST performed, I'd stop by the Church
. Anyway, I read about the brake switch and the tranny neutral switch from the 500E board and am not sure they will help.
MCELROYB, your problem seems to be more like mine. Have you had any success??
AMG280 - I'm gonna go get a Analog Volt meter,read/print the article and hopefully hit paydirt soon