1997 940 Idle Control Valve

[TonyS9]

Sounds like there are possibilities with the wiring. The abs checks the sensors are working, but you should double check them by unplugging and checking for resistance. I'd start by scoping the speed signal going into the ECU while driving, or maybe wheels off the ground. The signal should be missing. Then it's a matter of tracing back to find where is missing from. The abs conditions the signal into pulses and passes them onto the speedo and fuel ECU.

I'll come back with the pin number or wire colour

[Laird Scooby]

Originally Posted by Laney760

I had assumed for years, from threads on there, that I needed to send away my clocks for soldering and that the car would be off the road for weeks and I wouldn't be able to get to work so now I am really confused.

Can somebody advise what I should get checked / replaced first in order to get rid of the high revving problem please?

Do you have cruise control Ellie and if so, does it work? If it does, the correct signal is reaching the instrument cluster.

Have a look at this thread of mine about repairing the fuel gauge on mine, many of the parts might also apply to your speedo but if you take the instrument cluster out (it's different on a 940 and there's a certin knack to a couple of springs either side of the surround) and clean all the connectors that the multiplugs go onto, the "fingers" in the multiplugs and then using a small thin tool, insert it under the bowed part of the contacts on the plugs and ease the contacts out to give the bow more of a curve.

You may find this cures the problem. It's something you can try fairly easily yourself but you'll need someone to explain how to remove the 940 cluster as it's different to my 760.

[Laney760]

Cheers Tony, Cheers Dave. One clue to the speedo problem? On a smooth surface motorway it will suddenly cut in and work for a while, until you reach a less smooth part of motorway when it will cut out again.

[Steve940estate]

Hi, just reading about your problem and I wondered how high the idle was when it was misbehaving ? Mine used to idle higher than normal if I didn't let the engine warm up a bit before driving away. I still haven't fixed it and thought it might be the gas sensor in the exhaust. I was going to get a new one to see if it helped as I think it was taking linger to warm up and read correctly. High idle in my cars was about 1200rpm though. .

[Laird Scooby]

Originally Posted by Steve940estate

I still haven't fixed it and thought it might be the gas sensor in the exhaust. I was going to get a new one to see if it helped as I think it was taking linger to warm up and read correctly. High idle in my cars was about 1200rpm though. .

The Lambda sensor in the exhhaust isn't used during warm up because it doesn't function until it gets hot. Don't replace it. The high idle doesn't sound that high on a cold engine but it depends how cold.

The most likely cause of your problem is the CTS under the inlet manifold between #2 & 3 inlet tracts.

[Laird Scooby]

Originally Posted by Laney760

Cheers Tony, Cheers Dave. One clue to the speedo problem? On a smooth surface motorway it will suddenly cut in and work for a while, until you reach a less smooth part of motorway when it will cut out again.

I'd try what i suggested with the plugs on the back of the cluster having red that Ellie. It sounds like a bad connection and those plugs are the most likely although there are other causes.

[Forrest]

I found with one of mine the occasional non-functioning speedometer could be “fixed” by pushing (not too hard) on the dash in the vicinity of the parking brake and ABS warning lights. The root cause is almost certainly a loose connection or dry joint. I discovered this fix by accident when I realised resetting the trip recorder sometimes influenced the fault.

Another 940 needed a firm whack to the top of the dash to get the instruments working until I eventually fitted a replacement PCB.

As I recall, yours is quite a late model so it should be possible to find a working dash to try as a replacement. Some of the model years around 1993 and 1994 had year-specific variants making it quite hard to find working replacements.

[TonyS9]

Originally Posted by Steve940estate

Hi, just reading about your problem and I wondered how high the idle was when it was misbehaving ? Mine used to idle higher than normal if I didn't let the engine warm up a bit before driving away. I still haven't fixed it and thought it might be the gas sensor in the exhaust. I was going to get a new one to see if it helped as I think it was taking linger to warm up and read correctly. High idle in my cars was about 1200rpm though. .

What exact point in the journey did you notice it was idling high? LH2.4 keeps the idle high after a cold start until it warms up and you stop after that. Again we don't know the reason for this, I feel it is a bug. I notice it using pulse and glide, but the designer didn't expect the car to be traveling in neutral alot. It is very odd that it stops when you stop.

The O2 sensor control mixture at idle not idle speed. You need more air to increase the idle speed, not more or less fuel.

The missing speed signal combined with WOT the idle goes to about 1800rpm in my experience

[TonyS9]

Originally Posted by Laney760

Cheers Tony, Cheers Dave. One clue to the speedo problem? On a smooth surface motorway it will suddenly cut in and work for a while, until you reach a less smooth part of motorway when it will cut out again.

You could try an old fashoned thump on the dash.

I had a similar car with an intermitted speedo for a family member, replaced the instrument cluster with a spare and it worked but later failed again. Never got to the bottom of it, would be consistent with a failing sensor or wiring problem.

BTW the speed signal coming into the ECU is pin 34 on the fuel ECU (behind the kick panel), wire colours can vary but on my 97 loom its was Purple-White. The Volvo information says it 'comes from the speedo', not sure if that is accurate, but it also would be consistent with a bad connection to your speedo from whatever connectors.

[Laird Scooby]

Originally Posted by TonyS9

You could try an old fashoned thump on the dash.


BTW the speed signal coming into the ECU is pin 34 on the fuel ECU (behind the kick panel), wire colours can vary but on my 97 loom its was Purple-White. The Volvo information says it 'comes from the speedo', not sure if that is accurate, but it also would be consistent with a bad connection to your speedo from whatever connectors.

The speedo connection would be this then :



It's difficult to see because it's a close-up (and the flash) but that track from that screw with the red crimp on it leads round to the "S" terminal which is the "S"ignal terminal for the speedo - note also the + and - connections next to it on the edge connector - these are the main ignition switched power inputs to the cluster.

That terminal i've used for an aftermarket cruise control is used by the later (LH2.4) fuel ECUs and also the OE fit cruise control for the speed signal.

If the speedo is disappearing and the idle is staying high, the common factor is the 3-pin plug on the back of the cluster for the speedo, specifically the speedo signal connection as the rest of the instruments are working.

Maybe the plug is on skew-whiff, making the + and - but not the Signal connection except sometimes and then when the road surface changes, vibration knocks it off again. Had that on a few of my 740s over the years.