Found this that may lead to Gilbertds’ thoughts….

Engine Coolant Temperature (ECT) sensor - (from99MY)

The ECT sensor is located at the top front of the engine, adjacent to the coolant outlet pipe. The sensor screws into a thread in the inlet manifold and incorporates a sealing ring between the faces of the sensor and manifold.The ECT sensor multiplug has four wires; two are thesignal and ground connections used by the ECM, the other two are used by the body control module(BeCM) for control of the temperature warning lamp operation on the instrument pack.The sensor contains two thermistors with negative temperature co-efficients; as temperature increases,the thermistor’s resistance decreases. The ECM receives a corresponding analogue input voltagebetween 0 and 5V.NOTE: The temperature / resistance characteristics of the two thermistorsdiffer, and so it is important to maintainthe correct pin-outs.The ECM uses the information received from the ECTsensor to make adjustments to the engine operatingconditions. The ECM ensures a richer air:fuel mixtureis available at lower block temperatures for good quality starts and smooth running. The mixture is then made leaner as the engine temperature rises to maintain low emissions and good performance.For NAS vehicles with secondary air injection, thesignal from the ECT sensor is monitored at engine start, to determine whether the conditions are coldenough to warrant secondary air injection to beemployed. The ECT sensor is then monitored to switch off the secondary air injection when therequired engine coolant temperature has been attained.

If the sensor fails, the ECM uses a substitute software routine that changes default value during warm up,based on the signal from the inlet air temperature sensor. When the software model reaches a coolant temperature of 60°C (140°F) the ECM implements a fixed default value of 85°C (185°F). The ECM coolant model also forms part of the diagnostics that is performed for detecting a temperature sensor fault, as well as open and short circuit tests.

Temperature Voltage
-50°C 5V
-20°C 4.8V
10°C 4.2V
40°C 2.8V
70°C 1.4V
100°C 0.6V
130°C 0.2V

NOTE: All voltages listed are approximate.

A coolant temperature circuit failure may result in the following symptoms:
• Poor cold and warm/hot starting and driveability.
• Instrument pack temperature warning lamp willilluminate.
• MIL will be illuminated.
• Temperature gauge reads excessively hot orcold.
• Cooling fan will not run
• SAI pump will operate at engine start up even when engine is hot (NAS with secondary airinjection system only).

I will try change the temp sensor.

Gilbert, Good point.....
Is the SAI system actually switching on when this happens?? If so, it is certainly
the problem. (now we need a solution!)
If it is not activating when warm, obviously it cannot be causing the problem?

I have never been aware of the system coming on after a cold start, and there is indeed a second temp sensor at the bottom of the Radiator for 99-02 Bosch systems. Possibly if this sensor is faulty, or has a bad connection, it could cause the SAI to erroneously activate?

You posted as I was writing.....
I think you are on the right track though.
Interestingly, My 99 does not have the additional temp sensor, whereas my 02 does.
Even though the 99 was manufactured in Sept? Hmmmmm??

If I were to start reading again at the first post I might guess that it started fine from cold due to running open loop fuelling and as soon as it warmed up and switched to closed loop fuelling it ran poorly due to a duff lambda sensor.

Sometimes error codes can be misleading.. If the code doesn't point to an electrical issue such as open circuit SAI system maybe the ECU error detection assumes an SAI fault (because SAI is active) when there is a mixture issue?

But if you did read from the beginning, or even from halfway through, you'd see that if he plugs the SAI pipe with his finger it runs normally...... Definitely a problem with the SAI system rather than anything else.

Do you have any diagnostics James? As you've found, the temperature sensor on the Thor is two sensors in one body (rather than 2 separate sensors on the GEMS). One feeds the dashboard temperature gauge while the other feeds the ECM. If you connect OBD diagnostics that can display live data and look at what engine temperature is shown. If it is obviously wrong, that is the problem.

I have the NANOCOM and I will check engine temps tomorrow and report.
Thanks