Nissan Repair: 300zx electrical, air intake hose, throttle position sensor

Question
hi I have a 91 300zx and Im having a small problem each time I press the clutch in or put it on neutral the rmp drop and it shuts off at first I thought that it was the battery so I changed it the I changed the alternator to see if that was the problem so now I dont know what could it be I tested the charging sistem and with the car off the batteries voltge was 13v with the car on at idle it was 14v and with the lights on on high and the stereo on the voltge drops to 12v can you help me

Answer
Ivan,

The throttle body has a couple of things that can cause this.  First, the throttle position sensor could be worn out and the setting at idle no longer works, telling the computer that it is at idle and for the idle air control valve to take over to maintain idle.  Second, there is a dashpot that slows the throttle plate from closing too fast at the las bit of travel to idle.  Lastly, the idle air control valve itself could be sticking.  Get a Haynes Manual and a digital volt ohm meter and check the throttle position switch first and clean the throttle body with carburetor cleaner.  You cannot run the vehicle since the air intake hose will be off so use the cleaner sparingly.  And, reconnect the air intake hose from the air meter to the throttle body before you attempt to start it.  Note, the car will be flooded from all that cleaner and it will take a few attempts to start it.  First, put your foot to the floor and then turn it over to get the cleaner out of the engine.  The second or third attempt to start the car should work normally, with no foot on the gas.  The charging system is fine from the note you sent.  I just think the idle is going too low as a result of the idle circuit.