The 2 biggest improvements in idle for my 300E was the O2 Sensor and Water Temp sensor. Replaced all other items including OVP, Plugs, Wires, Voltage Regulator, Vacuum Lines, Distributor Cap, Rotor, and Coil with no change. Still need to try Idle Control Valve and then injectors and all the tough stuff. Once in a while, the idle still struggles for "I don't know what reason". Just my FYI Stuff