I don't think he meant speed sensor. The pre 91 doesn't have one. I think he meant ais. The settings all need to be adjusted and by adjusting them you check to make sure they are working correctly. Got the pm but it sounds like you are doing ok. If you need more help let me know. Finding a replacement for the ait is difficult but the coolant temp sensor is a good replacement of you can get a connector for it or solder it.
Here is the adjustment procedure for the ISA from the book:
IDLE SPEED ACTUATOR (ISA) MOTOR
1) Adjust ISA motor plunger to establish initial position of
plunger only if motor has been removed or replaced. Remove air filter
elbow and start engine. Run engine until engine reaches normal
operating temperature. Turn A/C off (if equipped).
2) Connect tachometer leads to diagnostic connector D1,
attaching negative lead to terminal D1-3 and positive lead to
terminal D1-1. See Fig. 4. Turn ignition off. ISA motor plunger
should move to fully extended position.
3) When ISA motor plunger is fully extended, disconnect ISA
motor wiring connector and start engine. Engine speed should be
3300-3700 RPM. If incorrect, turn hex head screw at end of plunger to
provide engine speed of 3500 RPM.
4) Fully retract ISA motor by holding closed throttle (idle)
switch plunger inward as throttle is opened. Closed throttle switch
plunger should not touch throttle lever in closed position. If
contact is made, check linkage and/or cable for binding or damage.
Repair as necessary.
5) Connect ISA motor wiring harness connector and turn
ignition off for 10 seconds. ISA motor should move to fully extended
position. Start engine. Engine speed should be 3500 RPM for short
period of time and then decrease to normal idle speed.
6) Turn ignition off. Disconnect tachometer. After final
adjustment of ISA motor, use thread penetrating sealant (Loctite 290)
on adjustment screw to prevent movement and maintain adjustment.
NOTE: If adjustment screw must be moved after thread sealant
hardens, loosen threads by heating screw with flameless heat
such as soldering gun. DO NOT use flame or torch type of