When first starting the car the service light comes on and then goes off after 5 minutes. When the car is idling the rpm's vary from 900-1000 and seems to have a slightly rough idle.

Clean the throttle body inside and the idle air control motor.This will help.

engine RPM must be near 800 not 400.
for all accessories to work , alternator, and P/S and A/C

so RPM is first.
next is belts must not slip.

the engine is running too slow. that is called bad idle controls
the PCM controls idle at all times perfectly
so its lost control and that is causes by 50 reasons.
get it serviced, is what you do.
or learn to fix cars. if you didnt notice low RPM then you need to learn that first.,

low rpm can be cause by
1: never getting a tuneup ever?
2: bad spark. weak or worse dead plugs.
3: bad fuelling, (too lean, or to rich misfiring)
4:bad engine, (50 reason) but can be vacuum leaks or ISC valve stuck closed, or EGR valve stuck open.

next time ALT lamp comes on , use your right foot to raise rpm to 800 or more, id bet the alt light goes out, and the P./S pump wakes up.

There may be an rpm adjusting screw on the throttle body its usually hidden inside a passage that has a metal plug over it. Its very rare you would need to reset the idle rpm, which is why its covered over. Check the idle speed on the emission label in the engine compartment and compare it to your reading, it should be pretty close but can vary a bit. The 0 oil pressure is another matter. You need to check the service manual to see what the min pressure is and at what rpm its to be measured. You can get all this info from the service manual Haynes or Chilton's your local library has access to their online manuals, and its free.

This should be a drive by wire vehicle meaning it has a cable for the throttle body. First thing would be to see if any error codes can be pulled up (most parts stores will do that for free.) Drive by wire versus the late model that use electronic control for the idle have a IAC or idle air control which when first started controls the idle air intake--all air is run by it to idle the vehicle when cold--

Usual symptoms are rather high idle when cold engine or even idle and RPM jumping up and down and stalling when cold.

Another way if idle does drop when cold is tapping the gas--engine will still run until hot. Means not usually a fuel pump issue.

You could also have if the vehicle is fuel injected a dirty Mass air flow sensor, a throttle position sensor, etc.

These can be if the vehicle has them cleaned using a special zero residue spray cleaner.

First have it scanned to see what if any errors it shows--the computer.

I would test both the tps and map sensors.
map sensor is here:



Testing

Check the Manifold Absolute Pressure (MAP) sensor circuit as follows:
Ignition OFF, disconnect the MAP harness connector at the MAP sensor.Ignition OFF, test for less than 5 ohms of resistance between the low reference circuit terminal 2 and ground.If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.Ignition ON, test for 4.8-5.2 volts between the 5-volt reference circuit terminal 1 and ground.If less than the specified range, test the 5-volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.If greater than the specified range, test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the ECM.Verify the scan tool MAP Sensor parameter is less than 1 kPa.If greater than the specified range, test the signal circuit terminal 3 for a short to voltage. If the circuit tests normal, replace the ECM.Install a 3A fused jumper wire between the signal circuit terminal 3 and the 5-volt reference circuit terminal 1. Verify the scan tool MAP Sensor parameter is greater than 126 kPa.If less than the specified range, test the signal circuit terminal 3 for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.If all circuits test normal, test or replace the MAP sensor.




Check the Throttle Position (TP) sensor circuits as follows:
Ignition OFF, disconnect the harness connector at the throttle body.Ignition OFF for 90 seconds, test for less than 5 ohms of resistance between the low reference circuit terminal C and ground.If greater than 5 ohms, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM. Ignition ON, test for 4.8-5.2 volts between 5-volt reference circuit terminal E and ground.If less than 4.8 volts, test 5-volt reference circuit for a short to ground or an open / high resistance. If the circuit tests normal, replace the ECM.If greater than 5.2 volts, test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the ECM. Verify the scan tool TP sensor 1 voltage is less than 0.1 volt.If greater than 0.1 volt, test the signal circuit terminal D for a short to voltage. If the circuit tests normal, replace the ECM. Verify the scan tool TP sensor 2 voltage is greater than 4.8 volts.If less than 4.8 volts, test the signal circuit for a short to ground. If the circuit tests normal, replace the ECM. Install a 3A fused jumper wire between the signal circuit terminal D and the 5-volt reference circuit terminal E of the TP sensor 1. Verify the TP sensor 1 voltage is greater than 4.8 volts.If less than 4.8 volts, test the TP sensor 1 signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM. Install a 3A fused jumper wire between the signal circuit terminal F and the low reference circuit terminal C of the TP sensor 2. Verify that the TP sensor 2 voltage is less than 0.1 voltIf greater than 1.0 volt, test the TP sensor 2 signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM. Ignition OFF for 90 seconds, disconnect the harness connector at the ECM.Test for less than 5 ohms of resistance on all TP sensor circuits between the following terminals:ECM C2 signal circuit terminal 65 to TP terminal DECM C2 signal circuit terminal 63 to TP terminal FECM C2 5-volt reference circuit terminal 3 to terminal E If greater than 5 ohms, repair the affected circuit for open/high resistance.Test for infinite resistance between TP sensor 1 signal circuit terminal D and TP sensor signal circuit terminal F.If less than infinite resistance, repair the short between TP sensor 1 signal circuit and TP sensor 2 signal circuit. If all circuits test normal, replace the throttle body.


Fig. Throttle Actuator Control electrical connector


Throttle Body Relearn Procedure
NOTE
Do NOT perform this procedure if DTCs are set.

Start and idle the engine in PARK for 3 minutes.With a scan tool, monitor desired and actual RPM.The ECM will start to learn the new idle cells and Desired RPM should start to decrease.Ignition OFF for 60 seconds.Start and idle the engine in PARK for 3 minutes.After the 3 minute run time the engine should be idling normal.
NOTE
During the drive cycle the check engine light may come on with idle speed DTCs. If idle speed codes are set, clear codes so the ECM can continue to learn.

If the engine idle speed has not been learned the vehicle will need to be driven at speeds above 70 km/h (44 mph) with several decelerations and extended idles.
After the drive cycle, the engine should be idling normally.

If the engine idle speed has not been learned, turn OFF the ignition for 60 seconds and repeat step 6.Once the engine speed has returned to normal, clear DTCs.

Here is the OBD2 emission system drive cycle test procedure.
Engine coolant temp must be below 70c (158f) before starting the engine for either the first or second trip
The fuel level should be less than 1/2 full
First trip:
Start engine, idle for at least 1.5 minutes
Drive 3 minutes, hold b/f schdl: 1.5-2.0 msec, selector lever "3rd" eng rpm 1,800-2,000 A/C switch:ON Hold the recommended b/f schdl range. Allow road speed to vary as necessary.
Drive at 55-65 mph for 1.5 min b/f schdl 2.0-3.2 msec, selector lever "5th" Engine rpm 2,200-3,000
IGN "off" for at least 10 seconds (not more than 5 min)
Dive at 50-60 mph for 3 minutes Selector lever "4th" keep engine speed above 3,000 rpm Allow speed to vary if necessary. Do not decelerate for more than 3 consecutive seconds. A/C switch ON.
Drive at a steady state cruise of 53-58mhp b/f schdl more than 1.8 msec selector lever "5th" eng rpm 2,400-2,600
Downshift to "4th" and decel more than 5 seconds without breaking, then idle for 1 minute.
Drive two minutes b/f schdl less than 2.0 msec Accelerate to 41 mph, decelerate to 34 mph, accelerate to 41mph. Do not completely release the accelerator. A/C switch off.
Idle 1 minute in park or neutral
Drive two minutes Steady state cruise at 31-44 mph. Selector lever "4th" A/C switch OFF. Hold the accelerator pedal as steady as possible. Allow speed to change if necessary.
End of first trip. Turn the key off the begin the second trip.
Second trip:
Start engine, idle for at least 1.5 minutes
Drive 3 minutes, hold b/f schdl: 1.5-2.0 msec, selector lever "3rd" eng rpm 1,800-2,000 A/C switch:ON Hold the recommended b/f schdl range. Allow road speed to vary as necessary.
Drive at 55-65 mph for 1.5 min b/f schdl 2.0-3.2 msec, selector lever "5th" Engine rpm 2,200-3,000
IGN "off" add four gallons of fuel
Dive at 50-60 mph for 3 minutes Selector lever "4th" keep engine speed above 3,000 rpm Allow speed to vary if necessary. Do not decelerate for more than 3 consecutive seconds. A/C switch ON.
Drive at a steady state cruise of 53-58mhp b/f schdl more than 1.8 msec selector lever "5th" eng rpm 2,400-2,600
Downshift to "4th" and decel more than 5 seconds without breaking, then idle for 1 minute.
Drive two minutes b/f schdl less than 2.0 msec Accelerate to 41 mph, decelerate to 34 mph, accelerate to 41mph. Do not completely release the accelerator. A/C switch off.
Idle 1 minute in park or neutral
Drive two minutes Steady state cruise at 31-44 mph. Selector lever "4th" A/C switch OFF. Hold the accelerator pedal as steady as possible. Allow speed to change if necessary. I especially like the part where they want you to add four gallons of fuel. Not three gallons, not five gallons, four gallons. Gotta love those Nissan engineers. ...and of course they state that if the trace is not followed exactly (i.e. you botch the acceleration/deceleration) you have to start all over again from scratch

The automatic idle speed control system has lost its adaptive idle learning due to the dead battery. To help to correct this in the short term run the engine at 2000 RPM until warm, then back down to 1500 RPM for 3 minutes, then 1000 RPM for 3 minutes, then let it idle for 5 minutes, this should get the system to a point in the idle learn that it doesn't stall out, then drive it for 20 miles under varied conditions of highway and stop and go and low speed operation, that should get all to work again. If you still have problems you will need to have the system scanned to see what is going on that is causing a stall. Also add fresh fuel, gas goes bad in about 3 months. Use the recommended grade of fuel.

Have you gotten good at driving with all three pedals?

I can think of two things that can cause this.

First, you make have a leak in your vacuum system. If your car just started doing this out of the blue, this is probably.

Second, if it has always done this, you can adjust the idle RPM speed by adjust the idle RPM control screw. This is located on top of the intake manifold right next to the end of where the large air hose goes on. There will be hole with a screw or a black circle cap that comes off with a screw underneath. Clockwise increases RPM at idle, Counterclockwise decreases RPM at idle.

Good luck!

this sounds similar to a problem i had. as the rpm went over 2000 the engine would stop for a split second and then kick back in.
after a few days looking my garage finally found the problem was a faulty air mass meter.
this cost me £200 in total to be repaired.

The Throttle Body Needs Basic Settings To Be Carried Out