The first rule of diagnostics is don't spend any money until you know what is wrong and that means careful and systematic checking and to give an example; replace the plugs if they are worn or fouled but make no assumptions so check the rest of the ignition system at the same time including plug wire resistance, cap, rotor, distributor vacuum units and then test the spark power.
Why change the fuel pressure regulator unless you know it is faulty and you can't know that unless you have done a fuel pressure and volume test - the diagnostic process isn't complete until such a test has been carried out and it is best to get it out of the way before you spend any money...
Check for a blocked cat converter
could be a problem EGR valve
SOURCE: 1986 Nissan 300zx ac only works when engine is iddling
the ac is supossed to slow down, it was a way for them to keep the torque there. there could also be a plug undone on the passenger side by the big black box there is a black container there for the ac that has two plugs one come unconected sometimes
SOURCE: the cilynder #1 and spark
Did you change the spark plug?? Your car (1993) has a distibutor assy, which means it has ignition wires for each plug. How are your wires??cap?? rotor?? Have you ever done ignition tune up?? If the answer is yes and you have already installed new injector and pressure regulator (althoug it still could be a injection issue/ECM or computer, because ECM is what drives the injectors. If the ECM or wiring to #1 injector has an issue, the injector will not fire off and put gas into the cylinder, resulting in a misfire.) Remove #1 injector connector and check to see if you have power/12V on one side of the connector. If you have 12V there, than check the other wire for continuity to the ECM. You will need wiring diagram to find the right wire color at the ECM. That other wire goes into the ECM to the driver which opens and closes the injector depending on your demands as far as gas pedal input. That driver may be bad, causing the injector not to shoot gasoline. Than I would be looking into a engine issue, such as burned valve, or head gasket problem (coolant getting into #1 cylinder, flooding your spark plug). Tough to diagnose over the computer and not looking at it my self. Let me know what you find.
SOURCE: Starting problem
Try the idle air control valve it is located near the throttle body it has a four wire plug and has two small hoses attached to it this is a small stepper motor that controls the amount of air on start up this part will cost about $200 from a popular auto parts store.
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Is that a turbo, or a non turbo? Do you know when, or how many miles it has been since the distributor cap, ignition rotor, and the spark plug wires were changed? They would also cause that condition and I did not see them mentioned, and they should at least be inspected for wear on the ignition rotor and button and for any corrosion on all of the terminals under the distributor cap, and the MAF sensor (Mass Air Flow) could also be the problem, and check for any air or vacuum leaks, or loose hose clamps in the air induction system, especially between the MAF sensor and the throttle body. Also check for a small vacuum line that runs out to the driver side fender well just below the ignition coil and connects to a MAP (Manifold Absolute Pressure) type of sensor.
I would recommend only STP gas treatment for your vehicle because it is one of the few treatments that will actually bond any water in the bottom of the fuel tank to the fuel inside of the fuel tank, so that any water build up in the fuel tank can be removed from the fuel system, and you can see it for yourself if you pour some gasoline into a clear container and then add a little water to the gasoline, and you will notice that the water drops below the gasoline and there is a visible line of separation between the two fluids, even if you shake the container the water will always separate back out of the fuel and they will not mix, and then put a few drops of the STP fuel treatment into the container and watch what happens, and you will notice that the fuel and the water will actually bond together and mix completely.
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