85 turbo - idle going crazy

Idle speed keeps fluctuating for no reason, way overspeeding sometimes.  Tried
swapping in a new throttle position sensor as this worked on another one of
these cars I had once, no change.  Also when car is doing this when first cold,
the speedometer starts reading off random numbers (??) but this seems to go
away shortly.   Am not getting any power loss light nor any stored codes.  It
definitely seems to be the computer telling the idle motor to increase
erratically - if I unplug the idle motor, idle stays steady forever until I
plug it back in, in fact I'm driving it like this now.   It seems to vary
between normal and various overspeeding, it is not making it go too low (not
stalling).  Any suggestion on what to check or change next?  Could it be either
of the sensors in the distributor?  I changed the rotor but thats it.  
thanks!...Mark