Weird Idling / Fan Noise

[CoreyGSD]

2008 Infinti g35 sedan - just turned 80k miles

a few months ago my car started doing this weird thing. When stopped and idling the rpm's fluctuate from about 1ooo down to about 500. It goes down for a couple seconds then back up, then back down and keeps doing this. As the rpms drop the fan turns on and it quiets down when they rpm's go back up. This starts happening when the car starts getting to temp. It never gets hot (my temp gauge stays just under half) and it never stalls. No check engine and it doesn't throw any codes when I run a OBDII scan.

I tried to find similar issues online but haven't been able to really see something just like this so I have been replacing parts like crazy. I have replaced my entire cooling system basically minus the water pump. I have replaced:

• - Fan unit with motor
  - Coolant Temp Sensor
  - Thermostat
  - Hoses
  - Air mass Sensors
  - Spark Plugs
  - Radiator cap

Frustration level is starting to build. I thought it might be the O2 sensor, but wouldn't it throw a code? Wouldn't I smell more exhaust in the air? I read somewhere that it could be that the idle needs to be reset by the manufacture possibly too?


Any ideas or help would be much appreciated.

[RED_DET]

You can try doing an idle relearn, the procedure is outlined below.

1. Perform 2003-2008 Infiniti G35 Sedan Accelerator Pedal Released Position Learning
A.Make sure that accelerator pedal is fully released.
B.Turn ignition switch ON and wait at least 2 seconds.
C.Turn ignition switch OFF and wait at least 10 seconds.
D.Turn ignition switch ON and wait at least 2 seconds.
E.Turn ignition switch OFF and wait at least 10 seconds.


2. Perform 2003-2008 Infiniti G35 Sedan Throttle Valve Closed Position Learning
A.Make sure that accelerator pedal is fully released.
B.Turn ignition switch ON.
C.Turn ignition switch OFF and wait at least 10 seconds
*Make sure that throttle valve moves during above 10 seconds by confirming the operating sound*

(Idle Relearn)
3. Start engine and warm it up to normal operating temperature.
4. Turn ignition switch OFF and wait at least 10 seconds.
5. Confirm that accelerator pedal is fully released, turn ignition switch ON and wait 3 seconds.
6. Repeat the following procedure quickly five times within 5 seconds. Fully depress and release the accelerator pedal.
7. Wait 7 seconds, fully depress the accelerator pedal and keep it for approx. 20 seconds until the MIL stops blinking and turned ON.
8. Fully release the accelerator pedal within 3 seconds after the MIL turned ON.
9. Start engine and let it idle.
10. Wait 20 seconds.
11. Rev up the engine two or three times and make sure that idle speed and ignition timing are within the specifications.