Strange Idle

The car P38 4.6 ticks over at about 1500 rpm when on choke then drops to about 1200rpm when the choke knocks off.. so I pulled the throttle position sensor (well I assume thats what it is, the front on the throttle body (opposite side to the throttle cable) there is a sensor which isn't vertical slightly towards 1 o'clock with a connector underneath it, anyway when I remove the connector the cars idle goes perfect to about 700rpm so I plug it back in and it stays the same until the following day where it starts doing the same revving up......
Someone mentioned to me it could be the Step Motor??

What do you think Guys??
Cheers Again
Daz

The idle air control valve is a stepper motor and they sometimes stick which is what yours sounds like.

Adjust the throttle cable so there is free play,if it still idles too high get the stored closed throttle voltage checked against the actual voltage.If the actual voltage at idle is higher than thestored value it needs resetting.