Nissan Repair: 94 sentra cold start, air control valve, coolant temp

Question
QUESTION: 94 1.6 sentra 5 spd  runs excellent when warm but when cold for the first 30 seconds it runs rough, it stalls sputters and all just short of dying. even if you give it gas it still won't help, done all the usual tune-up and check for vac leaks (can't find any) clean aiv thing and no differnce , and adjusted the idle, i am pulling my hair outon this one  thanks   Allen

ANSWER: Allen,

I would think, of yours is a carburetor model it would be the power valve that is electric inside the carburetor.  If yours is fuel injected check the idle air control valve.  Remove it and clean it and the passage and reassemble.  Disconnec the battery first and then hook it back up after you have the idle air control valve reinstalled.

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QUESTION: thanks for the response, it is fuel injected and i have tried and cleaned the idle air valve and adjusted it and it made no difference  thats why iam stumped thanks Allen

ANSWER: Allen,

Then, from what you have said, I think the cold start sequence, from initial start, is not activating.  The computer uses a temperature sensor to let it know to richen up the fuel.  This is like a choke on an old carbureted car.  The exception here is the computer increases the injector pulse width and that is how it richens up.  If yours is not richening up when it is first started the most common problem is the temperature sensor feeding data to the computer.  It is a pain to diagnose since it will not set a code and unless you have a Nissan Consult Scantool it is difficult to identify.  You could use a volt/ohm meter to probe the temperature sensor but it is around $20 bucks to just change the sensor.

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QUESTION: if your talking about the coolant temp sensor i already changed that.  i think there is a egr intake temp sensor ? is that the one you are talking about  

Answer
Allen,

There are a couple of temperature sensors.  One feeds the gauge and light and the other runs the fans and feeds information to the computer.  If you disconnect the EGR you might find that it is being allowed to open before the engine reaches operating temperature and that could cause off idle stalling.  But, it would not allow the EGR to open at idle regardless of it being cold or at operating temperature.  The way the EGR works is it will only open when the engine is at operating temperature, off idle and or steady state.  When you let off the gas the unit closes.