Idle Air Solenoid disconnected & it runs better

Recently I resorted to having our '91 300E checked on the new Sun computer system. Symptoms: Starts well when completely cold engine, but has a little roughness at idle, and if idled for an extended time with warm engine will occasionally bring on CE light, but starting the engine after warmed up will take a time before rpm stabilizes, and might even die when placed in gear. Get the car moving however, and with the exception of a little roughness at idle, everything is fine. Car has new fuel injectors, engine coolant temperature sensor, plug wires, Copper plugs, rotor and cap, and is not leaking around the fuel distributor's vertical metering shaft (whatever it is called). The idle air solenoid was also replaced along with the rubber hoses to and from it.

The roughness on idle seems improved, and the hot start, rpm hunting, and dying when first placed in gear, all these are not a problem when the idle air is disconnected.

Any suggestions would certainly be appreciated. Maybe the new idle air was defective, but it does operate in both directions, when checked on the bench.