Cold start idle problem - Page 2

mjk164 · May 4th, 2012, 07:35

It depends on the water temperature. As a rough guide, between the two ECT terminals there should be the following resistance readings:-
0deg C 5500ohms
20 C 2500 ohms
60 C 600 ohms
100C 180 ohms
If you get something like these then the ECT sensor is OK.
On my 960 with very similar cold start symptoms, it also threw up codes saying the ECT was wrong but it has no means of showing if there is a lack of 2 or 3 volts at the IAC valve. When I checked there was nothing wrong with the ECT. The radio supression relay supplying volts to the IAC and injectors is a known regular failure area as it has a high rating and easily semi-fails when having to pass high current through it.
A thought; I think the two ECTs are the same so, if you swap them round and the temp gauge is OK and the car runs the same from cold....then the problem is with the IAC.

Steve940estate · May 4th, 2012, 10:12

I've just ordered a gauge sensor for my 940 and it's different from the ECU one. I hoped it was the same as I have a spare one of those, no such luck though.

Interesting to read about the Suppression relay. I know they can affect starting if the start playing up but didn't know about them controlling the IAC valve. I have a strange idle problem I have never got to the bottom of where after a cold start the idle speed is too fast, doesn't do it if you leave the car idling for a while before driving it. I suspected the Lambda sensor but might check the supression relay to see what the voltage is.

The relay is on the battery side of the car, turbo and non turbo are different, and is fitted on the inner wing just in front of the strut tower.

Tankbuster · May 4th, 2012, 10:53

Quote:

Originally Posted by mjk164

It depends on the water temperature. As a rough guide, between the two ECT terminals there should be the following resistance readings:-
0deg C 5500ohms
20 C 2500 ohms
60 C 600 ohms
100C 180 ohms
If you get something like these then the ECT sensor is OK.
On my 960 with very similar cold start symptoms, it also threw up codes saying the ECT was wrong but it has no means of showing if there is a lack of 2 or 3 volts at the IAC valve. When I checked there was nothing wrong with the ECT. The radio supression relay supplying volts to the IAC and injectors is a known regular failure area as it has a high rating and easily semi-fails when having to pass high current through it.
A thought; I think the two ECTs are the same so, if you swap them round and the temp gauge is OK and the car runs the same from cold....then the problem is with the IAC.

Thanks.....will be doing some more diagnostics today.

Tankbuster · May 4th, 2012, 10:55

Quote:

Originally Posted by Steve940estate

I've just ordered a gauge sensor for my 940 and it's different from the ECU one. I hoped it was the same as I have a spare one of those, no such luck though.

Interesting to read about the Suppression relay. I know they can affect starting if the start playing up but didn't know about them controlling the IAC valve. I have a strange idle problem I have never got to the bottom of where after a cold start the idle speed is too fast, doesn't do it if you leave the car idling for a while before driving it. I suspected the Lambda sensor but might check the supression relay to see what the voltage is.

The relay is on the battery side of the car, turbo and non turbo are different, and is fitted on the inner wing just in front of the strut tower.

....So, the 2 sensors are different? Is that easy to note with them removed.....do the look much different?

Steve940estate · May 4th, 2012, 19:43

Quote:

Originally Posted by Tankbuster

....So, the 2 sensors are different? Is that easy to note with them removed.....do the look much different?

The shape of the electrical connectors are different.

This one is the one thats connected to the ECU.

Steve940estate · May 4th, 2012, 19:52

This one is for the temperature gauge and is fitted nearest to the front of the engine.

Tankbuster · May 6th, 2012, 11:10

Quote:

Originally Posted by Steve940estate

This one is for the temperature gauge and is fitted nearest to the front of the engine.

Thanks for info. Don't suppose you have a resistance chart for the gauge sensor? Have some info.....•Cars from 94 on: 75 ohms to get a 90C reading at the gauge (range: 780 ohms at 20C/68F to 75 ohms at 90C/194F)

Tankbuster · Jun 6th, 2012, 13:53

Hi. Just thought i'd post the solution. Faulty Engine Coolant Temperature(ECT) Sensor (the one that interfaces with the Engince Control Unit (ECU))

This is the sensor that screws into the cylinder head and is the one closest to the rear of the engine.
The one nearer the middle of the engine is the sensor that 'talks' to the temperature gauge.

The 2 sensors are not the same so be sure to order the correct one. The one for the temperature gauge has round electrical connection pins, whereas the ECT ECU interface has small flat electrical connection pins.

I can uderstand why some may get frustrated trying to diagnose related faults as there's a fair bit of checking/cleaning to do along the way.
Don't forget the basics, be systematic....you will find the fault!

May 4th, 2012, 07:35	#11
mjk164 VOC Member Last Online: Yesterday 20:37 Join Date: Aug 2006 Location: Hounslow West London	It depends on the water temperature. As a rough guide, between the two ECT terminals there should be the following resistance readings:- 0deg C 5500ohms 20 C 2500 ohms 60 C 600 ohms 100C 180 ohms If you get something like these then the ECT sensor is OK. On my 960 with very similar cold start symptoms, it also threw up codes saying the ECT was wrong but it has no means of showing if there is a lack of 2 or 3 volts at the IAC valve. When I checked there was nothing wrong with the ECT. The radio supression relay supplying volts to the IAC and injectors is a known regular failure area as it has a high rating and easily semi-fails when having to pass high current through it. A thought; I think the two ECTs are the same so, if you swap them round and the temp gauge is OK and the car runs the same from cold....then the problem is with the IAC.

May 4th, 2012, 10:12	#12
Steve940estate Steam Driven PC Owner. Last Online: Mar 4th, 2024 23:50 Join Date: Dec 2004 Location: Not sure.	I've just ordered a gauge sensor for my 940 and it's different from the ECU one. I hoped it was the same as I have a spare one of those, no such luck though. Interesting to read about the Suppression relay. I know they can affect starting if the start playing up but didn't know about them controlling the IAC valve. I have a strange idle problem I have never got to the bottom of where after a cold start the idle speed is too fast, doesn't do it if you leave the car idling for a while before driving it. I suspected the Lambda sensor but might check the supression relay to see what the voltage is. The relay is on the battery side of the car, turbo and non turbo are different, and is fitted on the inner wing just in front of the strut tower.

Jun 6th, 2012, 13:53	#18
Tankbuster Junior Member Last Online: Dec 26th, 2020 09:26 Join Date: Nov 2007 Location: Strathaven	Hi. Just thought i'd post the solution. Faulty Engine Coolant Temperature(ECT) Sensor (the one that interfaces with the Engince Control Unit (ECU)) This is the sensor that screws into the cylinder head and is the one closest to the rear of the engine. The one nearer the middle of the engine is the sensor that 'talks' to the temperature gauge. The 2 sensors are not the same so be sure to order the correct one. The one for the temperature gauge has round electrical connection pins, whereas the ECT ECU interface has small flat electrical connection pins. I can uderstand why some may get frustrated trying to diagnose related faults as there's a fair bit of checking/cleaning to do along the way. Don't forget the basics, be systematic....you will find the fault!

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