Hi all, I was hoping that someone might be able to assist with understanding the 5v reference circuit.

I am getting some unexpected test results and could really use some help to understand what it means.Tests run on my 1998 Disco i (NAS) with ABS and Charcoal Filter (100k miles)
Computer: MKC104620

SYMPTOMS

• High Idle (1,500 to 2,200RMP)

TEST RESULTS

• Intake Air Temperature Sensor Reporting -36F (actual under hood temp 165F)
• Intake Air Temperature Sensor Tested Unplugged reading 440 OHMS (appropriate for 165F)
• Intake Air Temperature Sensor Red-Black Wire Tested Unplugged from sensor with key in 'On' (3rd position) 0.002V
• Intake Air Temperature Sensor Grey-Light-Green Wire Tested Unplugged from sensor with key in 'On' (3rd position) 5.0V
  
• Unplugged all 6 sensors on the shared 5v reference circuit and tested again achieving same result (Red-Black Wire has 0.002V)
• With all sensors still unplugged and with the key still 'On' I tested the wire at the ECM (Connector C1017) and saw the same 0.002V
• With the Battery negative disconnected I disconnected Connector C1017 and tested the resistance of Red-Black Wire and found that to all sensors the resistance was zero OHMS

6 Sensors on the Shared Reference Circuit

• Intake Air Temperature Sensor
• Engine Coolant Temperature Sensor
• Engine Fuel Temperature Sensor
• Throttle Position Sensor
• Mass Air Flow Sensor
• Camshaft Position Sensor

I've pulled some images together from available diagrams:

 

assuming you are trying to solve the high idle issue.....what else have you done maintenance wise to the vehicle...cleaned the iacv ?, checked for vac leaks ?.....a few of us with these confounded "advance evap " vehicles have also had issues with the fuel tank pressure sensor...or the wiring to it....developing a short and causing poor information being fed to the ecu.....because the pressure sensor is tied into the same circuit as the TPS.....a quick way to eliminate the tank sensor is to just unplug it at the fuel pump and see if the issue changes any, worth a look

 

Thanks XCELLER8!

I believe my Disco has the Advanced Evap system and was unaware that the pressure sensor for it was part of the same circuit. I will look into it straight away unplugging as you suggest.

I did replace the IACV (following procedure for the computer to relearn the new sensor).

The thing that keeps getting me is that it seems the Red-Black wire should have 5v running through it... Or does the system in the rovers work differently?