With your gauge reading at idle with the fans in low mode your reading is in range of expected , it being above 88 C for close loop mode

 

Removing the connector on the 2 wire ECT sensor how many ohms resistance do you read ?

It can be compared to a chart on page 78 of the Jaguar 801s PDF

Your gauge reading of 91 C should be around 250 ohms

The thermostat is set for just above the 88 C and not the blue marking on the gauge, so I see no coolant temp or flow issue

Looks like a hot beverage thermometer

 

200 ohm setting is not giving me a reading.
i have to put it onto continuity setting. I assume that is 20 ohm setting and i was getting a reading of 280

and yes that is a hot beverage thermometer. Though it would be accurate enough to give a good idea.

 

With your meter range in the proper place and the reading of 280 ohms , is in range to have an accurate ECT sensor

 

yeah looking at the guide 280 seems to be around 85c

this is still not helping me find the issue. Darn it.

 

The air temperature sensor may have stripped the threads in that plastic elbow. You might want to find a replacement on eBay or something. I’d be worried about vacuum leaks now.

The following items need to be read by the ECU to enter closed loop:

1. TPS
2. MAF
3. Oxygen Sensors
4. Coolant Temp Sensor

If one of those sensors is not providing data within expected ranges, ECU stays in open loop.

You can trick the Coolant Temp Sensor by jumping the two contacts on the harness when you disconnect it.

When was the last time you replaced the oxygen sensors? They do wear out and should be replaced every 60,000 miles.

Driving in open loop does result in terrible fuel economy; so you’re on the right track….

 

contained in this thread is all the details about the o2 sensors.
i changed them on the 28th August.

it does appear that the temp sensor is reading properly but i will try jumping the contacts to see if it makes any difference.

it appears the TPS is reading correctly as the torque app is showing 10.59 at idle right up to 100% with WOT. and i have confirmed by adjusting throttle cable and visually checking butterfly to confirm it is opening and the reading appears to match how much it is open. it reads 10.59 but the butterfly appears fully closed. i assume this is correct.

i have cleaned the MAF so i think it is working correctly but am not sure how to test/check.

i would like to get a vacuum tester and test for vacuum leaks but i do not have anything to do that with.

the sensor in the elbow appears the plastic part has broken off the metal thread and is spinning but not actually loosening. i have wrapped some silicone tape around it and put a cable tie there also just to ensure it is not leaking even tho i am sure it is not
same thing has now happened to my coolant temp sensor as when i went to remove it the plastic part is turning and turning but the thread is not loosening at all. and i know here that it is still sealed as there is no leaking.

 

ok, so i just used a wire to jump the coolant temp sensor plug and it actually made the idle worse. the car was more reluctant to start than i have seen it ever, sort of spluttered a bit and then the idle in park began to climb past 1400.


all this messing around i am doing and i will probably find its a vacuum leak. i can't see or find anything obvious. but who knows.
or it will be the idle air control valve.

 

On your ECU connector socket Red 14 and Red 31 you should see the same 280 ohms resistance after you have warmed the engine up

You would have to do the reading quickly after engine shut down and coolant cool down for accuracy

This would be what the ECU sees to get your closed loop mode and verifies a not bad connector sockets and wiring between , there are no wire splices in between the sensor and ECU

By taking a paper clip and 0 resistance for sensor value the ECU may be rejecting the sensor value and go into a limp mode

Send a pic to verify correct meter switch selection to be sure

Your 280 value is right on the edge of the 88 C for closed loop, but the accuracy error and meter calibration of the reading may be a factor

2 / 100 ohm resistors in series at the ECT sensor connector will be in an expected range and you may see on your device closed loop

You might be at a thermostat part change and is important that no O - ring on installation as parts from the vendors get mixed around

The X300 uses no O - ring because it cracks the thermostat housing casting as you clamp it down

 

If you jumper the coolant temp plug that tells the ECU the engine is full hot. I'm not surprised it was hard to start, I'm actually surprised it did start.

 

The reading i was getting at 280 was a little while after the car was running so it would have cooled down a little.
i tested again a little later and it was reading 300.
so the sensor does appear to work
after next drive i will test immediately to see where it is at.

i have a spare sensor so what i might do is full a cup with very hot water and see that sensor and see what happens…

is there an easy way to test the operation of the idle air control valve?
i would think it is working atleast to a point as if i disconnect the coolant temp sensor the idle will rise a lot. That indicates to me that it is opening up but maybe it cannot close enough so it cannot change the idle when car is hot



@Parker 7 on the continuity/lowest resistance setting.
200 ohm gives no reading as its too low resistance.

 

300 ohms puts you under the 88 C tipping point for close loop

this doesn't point to the sensor as it does seem to respond

The continuity test position with the diode symbol is not the best meter switch position

try the 2k ohm position

The sensor is a thermistor which is a solid-state device that has to be powered by a 9 volt battery powered meter which yours looks most likely and not a micro sized meter powered by 1.5 volt batteries

The IAC valve motor is hard to test in practice as they most likely fail when the stepper motor is heated and ex[anded as well as tapping on it

 

i will try it on the 2k setting. i just figured if it got no reading on the 200 then going to continuity was btte than the 2k setting.

i will be headed to my car soon and will test my spare sensor using hot (almost boiling) water and see what reaction i get.
to determine if maybe the sensor is reading correct but the car is not reaction to the reading

 

Your readings are too close to either side of the 88 C tiping point

This points to a new thermostat if no faults found in the wiring condition and timely / accuracy reading precautions

Did you get a EML 327 device ECT temperature that corresponds to your meter resistance readings ?

 

thermostat is new......
the readings may be too close to the tipping point due to not being warmed up long enough? i dunno...
i replaced the thermo cus when i had heater issues i thought, maybe its stuck open. so just replaced it....

how long should it take for the car to warm up?

 

Ok.
so yes the car is not getting hot enough…..

Old the temp sensor i replaced a little while ago when diagnosing the heater.
sitting in hot water…….

connect it and car idle drops…..
it enters closed loop and idle runs lower…..

 

Brillant, like your test setup

Time for test drive keeping in mind the Thermostat ( even new ) may be regulating at too low of a temp and be back in open loop true coolant temp range

 

Although just did the same test again,

and the idle is not dropping…..

 

When the ECU loses a sensor it will revert to a less then optimal mode of regulation

It takes some time ( or cycle ) after it sees a good sensor to revert back to optimal

 

Ok so now i need help asap. I took out the iac to clean it.
i plugged it back in and the the thread pooped all the way out. What do i do now?
it is too far unthreaded for it to sit back in now