Nissan Repair: 1990 240sx, haynes manual, vavle

Question
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Followup To
Question -
We have purchased a 1990 240sx for my daughter. After we bought it, the air-conditioner went out and we replaced the compressor which fixed that problem. But after we changed it out the car starting idling real low and will stall at times.  We have changed the plugs, changed the fuel filter and changed the air filter and the problem still continues.  No one can tell us what we need to do to correct this problem, can you help?
Answer -
If the idle problem is when the airconditioner is on there is something pulling the system down like an overcharge condition or a defective compressor.  You can check this out by disconnecting the belt to the compressor.  If the problem goes away you have isolated the problem.  If it is just happenstance you could have a bad distributor.  My daughters car had similar problems and it was around the time I changed the compressor.  it turned out that oil was getting in the distributor in the optical sensor under the cover that is under the rotor.  Well, a rebuilt distributor solved the problem.  But, in your case please check the airconditioner compressor first.
Question:
I failed to tell you that the car only idles low or stalls when the air-conditioner is turned off.  If it is on it seems to run fine.  Could this still be the distributor?  We have researched and found several different solutions.  AAI valve, AIC valve-could this be the problem and how would we know?  Is there a test that can be run to determine this?  Thanks

Answer
Yes, it could very well be the air vavle or the throttle position switch.  Check the air vavle and adjust it with a screw deiver on the end to increase the idle of the car if it will not increase the speed you might get a Haynes manual and check for correct voltage to the throttle position switch.  As old as it is the contacts could be corroded and if that is the case you would replace it with a new one.