Nissan Repair: Un-even idle, blower motor, couple questions

Question
QUESTION: I have an '89 D21 pickup with the VG30i engine.  The engine is in good tune and still runs very smoothly but, as of lately it seems to hunt for an idle speed even when the engine is warm (with blower moter turned off).  RPM range varys anywhere from 900 to 1200 at idle.  Could this be a sensor that is going out and if so, which one?

Thank You in advance
Scott

ANSWER: Hi Scott -

I have a couple questions, please bear wioth me as obviously I can't be there to diagnose -

1. Is you check engine light on?

2. When you say blower motor on, does this mean A/C?

3. If so, does it only surge when the blower is on?

Let me know -
aloha
calvin

---------- FOLLOW-UP ----------

QUESTION: Calvin,
Thank You for the quick response, as to your inquire... no, the Check Engine light is not on (this vehicle was not equipped with a Check Engine light) and the truck does not have A/C.  The blower motor in question is just for heater/defrost, vent.  With the blower motor turned on there is a little more drag on the engine so a slight increase in RPM would be expected here.  The un-even idle occurs wheather the blower is on or off.

Thanks again
Scott

Answer
Hi Scott -

OK - I think this year (89) the engine's idle speeds are controlled by solenoids. Find the idle speed solenoid and disconnect it. See if the idle speed is then constant. If so, it could be a defective solenoid. Is this car carbureted?

Thanks
calvin