940GLE' 91 CEL and high idle

bobbyz · Post by **bobbyz** » 05 Nov 2008, 16:20

Previously the car had hot stall problem, until I replaced the fuel pressure regulator, when the problem went away.
Today, out of the blue it threw a Check Engine Light! Instead of stall problem, now the idle goes to 1500rpm after the car’s driven for a while. If I turn it off, let it cool down & start it up, the idle goes back to normal. CEL stays on.
After driving for a while, the idle stays high again.
I checked the code, and it's giving me 2-3-2, which is what I got when there was hot stall problem!

Any advice is greatly appreciated.

Post by **billofdurham** » 06 Nov 2008, 15:53

Although you have a 2-3-2 code which indicates lambda adjustment have you checked the throttle switch which is one of the causes of erratic idling in a hot engine? Also check the coolant temp sensor that sends info to the ECU, not the gauge.

Bill.

bobbyz · Post by **bobbyz** » 07 Nov 2008, 15:38

Cleared the CEL last night.
This morning, it started with high idle (1400rpm). Then idles went to normal after driving for 5 minutes. CEL came back.
Cleared CEL, but it came back minutes after driving the car, although idle was ok. No stalling, hesitation, strange noise, black smoke or gas smell.
Can faulty TPS or ECT throw a CEL? Why did CEL come on when idle was OK?

Post by **billofdurham** » 07 Nov 2008, 15:58

Both can cause a problem that will put on the CEL.

If the coolant temp sensor is faulty it will send false info to the ECU which will then try to adjust the fuel/air mixture. If this adjustment is excessive it will set a fault code, usually related to the Lambda which will be reading rich or lean mixture.

To test the coolant temp sensor disconnect it and put an ohmmeter across the sensor terminals.
At 14F (-10C) the reading should be 8,260 - 10,560 ohms.
At 68F (20C) the reading should be 2,280 - 2,720 ohms.
At 176F (80C) the reading should be 290 - 364 ohms.

This relates to the CTS that feeds info to the ECU, not the gauge.

To check and adjust the TPS open the throttle slightly and listen for a click which should be heard as soon as the throttle opens. If it appears to be out of adjustment loosen the mount screws, turn the switch slightly clockwise and the counterclockwise until the switch clicks. Tighten the mount screws and re-test.

Bill.

bobbyz · Post by **bobbyz** » 07 Nov 2008, 19:16

Thanks Bill for the info.

According to Brickboard, the ECT sensor is somewhere near cylinder 3, which is quite far back, close to the firewall
I have a pix here, there's a sensor with white connection on it, the sensor is on the left of coolant temp gauge sensor. Don't know the colors of wires in it since it's sealed in.
This sensor is actually pretty close to the front, near cylinder 2 or 1. The bulbous metal part on the left of the pix is the thermostat housing.
Is this really the ECT sensor? Its location sure contradicts what the Brickboard states

Any clarification would be greatly appreciated

Post by **billofdurham** » 08 Nov 2008, 11:15

What you have read on Brickboard is word for word what is on Swedishbricks and Volvo Club UK who all seem to pas the info around.

Being technical the gauge unit is a temperature sender and the ECU unit is a temperature sensor. There is a subtle difference between the two.

In your picture the grey coloured unit with the black/yellow and white/yellow wires is the temperature sender for the gauge.

The sensor for the ECU has grey/white and red/black wires and I believe it is the unit in front of the other, contrary to what is on the other forums. That rubber sleeve will peel back to expose the wires so it is easy to confirm.

I am sorry I can't be more specific on this as it is something I have not replaced on any of my Volvos, fortunately.

Bill.

bobbyz · Post by **bobbyz** » 09 Nov 2008, 14:59

Thanks for the clarification Bill.

I checked the sensor connection today, and it just slipped off in my hand! What must have happened was that I didn't plug it back properly when I was checking this sensor couple of days before CEL came on, though I wasn't sure what it was. It was a pain to plug/unplug.
btw the cable sheath is so tightly wrapped I couldn't peel it back to check the wire colors, I think I'll just leave it for now.
Cleared CEL, plugged it back properly and took it for a drive. Everything is normal now.
At least I know now where the ECT sensor is and what it's like driving with the sensor off!

The CEL was a shocker to me, since it didn't come on when the car was hot stalling like crazy previously.
It's also a surprise to find that the sensor is in a different location than what was stated in the forums.

Post by **billofdurham** » 09 Nov 2008, 15:15

Thank you for the update.

Good to know you have put it right, even if it was by accident!

the sensor is in a different location

I have only one diagram of the sensors on the 940, 1995 model, and it shows the coolant temp sensor towards the front of the engine. The temp gauge sender is between cylinders 2 & 3 but nearer to 3. I did wonder if the earlier models were in a different location.

Bill.