1997 940 Idle Control Valve

[Laney760]

I think I need to replace my idle control valve or have it cleaned? Can anyone point me to it's location please?

I posted about my problem on here donkeys years ago, but can't find the thread now. After I come off the motorway the car idles far too high and I have to turn off the ignition and restart for the idle to sit where it should. Several times I've thought the problem has gone away after the fitting of various parts but it hasn't and now it is getting worse, it will do it even after I've given the car a bit of welly overtaking.

I hope you are all keeping well, I hardly have time to be on here these days, working long hours still, I've worked right through the pandemic, I'm probably lucky to still have my job. Stay safe everybody

[taiwan740]

If you follow the air hose from the air filter housing to the intake, on the intake side about 12"/30cm below the air hose. There

https://www.youtube.com/watch?v=rSdbJ4nMa4M

Is the silver thing in the rubber bracket just north of the alternator in this video

[TonyS9]

This won't be caused by the IACV. The ECU is doing deliberately. The fact that a reset is fixing it indicates there is nothing wrong with the IACV.

For reference the IACV is under the inlet manifold.

You need to read the codes, they may tell you what is wrong.

For example a missing speed signal can cause this, but also erroneous AC on or auto drive select signals.

[Laney760]

Originally Posted by TonyS9

This won't be caused by the IACV. The ECU is doing deliberately. The fact that a reset is fixing it indicates there is nothing wrong with the IACV.

For reference the IACV is under the inlet manifold.

You need to read the codes, they may tell you what is wrong.

For example a missing speed signal can cause this, but also erroneous AC on or auto drive select signals.

Aaahh! Codes are all clear, bar the one for the speedo, speedo doesn't work. So its because my speedo doesn't work? Can't remember what code I always get, will read them again later, but it's always the one for missing speed signal.

[TonyS9]

Yes it will be the speedo signal. The ECU is saying it isn't getting a speed signal.

Its noticed by the 360 turbo upgraders, when you use full power with no speed signal the ECU punishes you with high idle. We don't know why. I've actually designed a speedo signal generator because the 300 doesn't have one with its mechanical speedo.

Anyway the fault maybe with your pickup or ABS, rather than speedo.

[Laney760]

Originally Posted by TonyS9

Yes it will be the speedo signal. The ECU is saying it isn't getting a speed signal.

Its noticed by the 360 turbo upgraders, when you use full power with no speed signal the ECU punishes you with high idle. We don't know why. I've actually designed a speedo signal generator because the 300 doesn't have one with its mechanical speedo.

Anyway the fault maybe with your pickup or ABS, rather than speedo.

Tony, please can you elaborate on '' maybe your pickup or ABS''? The speedo hasn't worked for a very long time but the idle didn't have this problem when the speedo first packed up.

I just did a forum search and found this thread, I've had a new lambda probe and coolant temp sensor, neither of them made any difference to my problem - https://www.volvoforums.org.uk/showthread.php?t=276927

[TonyS9]

Its possible the speedo failed first then the sensor, but maybe the sensor was working occassionally or with reduced signal so the speedo didn't work but the ECU still detected it. The speedo needs an accurate signal, the ECU only needs 'any' pulses.

We need to address the speed signal, then maybe both faults will be cured, but fixing the speedo will probably not fix the missing speed signal.

Does your car have ABS, and is it working?

Normally it the ABS sensors that are used for speed, maybe in the rear axle.

[Laney760]

Originally Posted by TonyS9

Its possible the speedo failed first then the sensor, but maybe the sensor was working occassionally or with reduced signal so the speedo didn't work but the ECU still detected it. The speedo needs an accurate signal, the ECU only needs 'any' pulses.

We need to address the speed signal, then maybe both faults will be cured, but fixing the speedo will probably not fix the missing speed signal.

Does your car have ABS, and is it working?

Normally it the ABS sensors that are used for speed, maybe in the rear axle.

Hi Tony. Which sensor are you talking about please? I have ABS and it works perfectly plus the codes show no ABS faults. The guy that sold me the car fixed the speedo when I returned the car for work once shortly after buying it from him, he carried out work behind the clocks, probably soldering on the circuit board, but it soon failed again, we are going back a long time now but last year when I was fiddling around fuses and relays and moving the wiring the speedo started working but the next time I was fiddling around with the fuses and touching the wiring the speedo stopped working again.

[Laird Scooby]

Originally Posted by Laney760

Hi Tony. Which sensor are you talking about please? I have ABS and it works perfectly plus the codes show no ABS faults. The guy that sold me the car fixed the speedo when I returned the car for work once shortly after buying it from him, he carried out work behind the clocks, probably soldering on the circuit board, but it soon failed again, we are going back a long time now but last year when I was fiddling around fuses and relays and moving the wiring the speedo started working but the next time I was fiddling around with the fuses and touching the wiring the speedo stopped working again.

Tony is referring to the speed sensor in the back axle Ellie, it provides a signal to the speedo and the ABS system and also the fuel ECU so it can control the idle speed coming down to prevent unexpected stalling.

As he rightly points out, the ABS just needs pulses, the speedo needs more defined pulses but to me it sounds more like an electrical problem with the instrument cluster, possibly the speedo, maybe the multiplugs on the back, could be dry joints on the PCB or a number of other things.

The AICV is working though or you wouldn't have the high idle and it wouldn't reset as Tony has already pointed out.

[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?