Nissan DataScan ?: Gauge Temp. or ECU Temp.

[sdkhalsa]

Have a question about Nissan DataScan. There is a temperature dial on the monitoring panel. Is this gauge temp. or ECU temp? I suspect a faulty ECU temp. sensor, as the idle which previously ran a very solid 750 rpm under all loads and temperature is now over 1000 when fully warmed. IAC seems to be fully functional with a duty cycle of 8% at idle with no accessories. Have checked carefully for vacuum leaks, incl. EGR, and have not found any. Still looking for Nissan DataScan Manual, if anyone knows of any.

[elwesso]

Itd be the ECU temp.... The computer doesnt know what the gauge reads, it just feeds the temperature gauge and the climate control (for coolant temp... all the climate control cares about is if the coolant is above/below 90F)

[Q45tech]

HVAC has its own water temp sensor, as does ecu, and the inside gauge.

3 coolant temp sensor in total......................the ecu reported temperature is probably the most accurate near 170-200F it is probably +- 2F accurate [1%] assuming the sensor is clean and not corroded [insulative effect]

ALSO TCS car have another [the 4th] coolant temp sensor to make sure coolant is warm before the TCS fully engages.

[sdkhalsa]

Thanks so much everybody. I think that it is time to track the temp. and IAC duty cycle at the time that idle starts to go into the high range. I would assume that if the duty cycle is normal, and if the IAC is not sticking, then the problem would be a vacuum leak. If the duty cycle is high, then you are looking at a sensor problem, like the temp., TPS, MAF. How does this sound?

[Q45tech]

The other thing one must be aware of that OVERRIDES the ecu is the engine warm up system [FIC] which cracks the throttle plate based on coolant temperature flowing thru [around] throttle body housing. THE FIC*

This overrides the IAC due to the great amount of air flowing under the cracked open throttle plate................usually ecu tries to add/subtract some to supplement the normal 1500 rpm in the beginning.

Be sure that the coolant is as least 174F and has stablized for 10 minutes before adjusting IAC manual bypass.

* FIC is difficult to adjust, better to not touch it period [because it cannot change by itself] unless you have ways to stablize the entire throttle body assemby at 32F, 77F and 174F........even a single turn can wreck havoc.