RPM surge problem when AC is on.

Vollic your 2000 model year S40 hasn't got an electronic throttle so there isn't an ETM. But blues60 is suggesting a general clean of the throttle butterfly, idle valve etc.

blues60, your problem intrigues me! Are you saying it ONLY happened when air con turned on, same problem like vollic has?

Vollic, there is no direct link between the air con and the throttle in the way I think you mean.

But what 4 forty is saying is that there is a sensor which automatically increases the idle to compensate for the increased load of the air con being on. So perhaps you could check and see if this is related to your problem.

What you could do is a simple test. Let the car idle, put temperature to cold and turn on air con. Based on your fault, the revs should now rise.

Now turn the car off, disconnect this compensation sensor and start the car again.

If the revs now rise straight away with the aircon OFF then you can conclude there is a problem with the sensor or the ECU or something which controls the idle speed. The reason is because disconnecting the sensor must be like when you turn the aircon on, so the idle thinks the aircon is on but in reality it is not.

If the revs don't rise, continue.

Now turn on the aircon.

IF the revs now do NOT rise then again you can be pretty sure the problem is somehow related to the electronics that control the idle speed. Maybe the sensor, maybe the ECU or something. (Note: you may well notice the revs actually FALL when the air con is turned on). In this scenario, having the switch disconnected is like with the aircon "off" so the ECU thinks it is off.

BUT if the revs still DO rise then there that is very strange and we will all have to think again...

Obviously to do this test, you need to know where this idle compensator sensor thing is so you can disconnect it! I don't know.

4 forty: do you know where the sensor is?
Pete

Pete s40,thanks!I'll give it a try your test method but i'll need to know where the sensor is.I also heard that by changing the thermostat and coolant sensor might cure this problem.I have doubts becos i don't see any sign of very high temp increase on my dash board.(always at 3 o'clock postion) which i think is normal.Whats your opinion?

vollic

Originally Posted by peteS40

Vollic your 2000 model year S40 hasn't got an electronic throttle so there isn't an ETM. But blues60 is suggesting a general clean of the throttle butterfly, idle valve etc.

blues60, your problem intrigues me! Are you saying it ONLY happened when air con turned on, same problem like vollic has?

Vollic, there is no direct link between the air con and the throttle in the way I think you mean.

But what 4 forty is saying is that there is a sensor which automatically increases the idle to compensate for the increased load of the air con being on. So perhaps you could check and see if this is related to your problem.

What you could do is a simple test. Let the car idle, put temperature to cold and turn on air con. Based on your fault, the revs should now rise.

Now turn the car off, disconnect this compensation sensor and start the car again.

If the revs now rise straight away with the aircon OFF then you can conclude there is a problem with the sensor or the ECU or something which controls the idle speed. The reason is because disconnecting the sensor must be like when you turn the aircon on, so the idle thinks the aircon is on but in reality it is not.

If the revs don't rise, continue.

Now turn on the aircon.

IF the revs now do NOT rise then again you can be pretty sure the problem is somehow related to the electronics that control the idle speed. Maybe the sensor, maybe the ECU or something. (Note: you may well notice the revs actually FALL when the air con is turned on). In this scenario, having the switch disconnected is like with the aircon "off" so the ECU thinks it is off.

BUT if the revs still DO rise then there that is very strange and we will all have to think again...

Obviously to do this test, you need to know where this idle compensator sensor thing is so you can disconnect it! I don't know.

4 forty: do you know where the sensor is?
Pete

For sure a failed (or disconnected etc.) temperature sensor could lead to high revving, but it has nothing to do with the aircon. As you say when the aircon is not on then the car does not do this revving up problem, then I don't see that the temperature sensor(s) can have anything to do with it.

Hopefully someone will know where this idle compensator sensor thing is...

Hmmm... I've just had a look at a VW workshop manual and it seems on the setup for a vw golf the engine coolant temperature sensor is used to provide information to the aircon about whether to shut off in the event of high coolant temperature.

If it is a similar setup on the S40 then maybe there is the possibility of some dodgy electrical problem causing the Engine management system to read incorrect values from the coolant temperature sensor when the aircon is on.

However this does sound very very unlikely to me, but it could be a possibility. Don't know a great deal about aircon specifically I'm afraid.

I suppose you could always do a further test which would be to:
- turn off car and turn off ignition
- disconnect the engine temperature sensor
- start engine
- note the revs. They might be quite high at this point.
- turn on air con
- see if revs change at all. If they do then probably this temp sensor can be ruled out as having nothing to do with anything
- turn off car, reconnect wiring

What engine do you have? Temperature sensor probably screwed into thermostat.

I'm searching for these 2 parts (thermostat and temp sensor) and have got the quotation.Its not very costly and i can replace it myself.I'll give it a try though i do not have signs of high temp indication.
I've traced the temp sensor wire and seems to me(i think!becos the wire is hidden in another bigger wire bundle)and this bundle is routed all the way towards the direction of the throttle body.May be this defective sensor sends wierd signal to the throttle.(i guess)
Mine is a 1.6 16v non turbo B4164 S2 engine.I'l try whatever solutions to find the fault.hopefully its simple.Btw i've located the temp sensor which is located at the top (coolant outlet hose) from the radiator to the engine body.The thermostat is inside(have to remove the fitting to see it) and the sensor is just beside it.It can be easily located.
But at the mean time hopes that some guys out there knows where the idle compensator sensor are....

Regards,
Vollic




Even if it was not the

Originally Posted by peteS40

Hmmm... I've just had a look at a VW workshop manual and it seems on the setup for a vw golf the engine coolant temperature sensor is used to provide information to the aircon about whether to shut off in the event of high coolant temperature.

If it is a similar setup on the S40 then maybe there is the possibility of some dodgy electrical problem causing the Engine management system to read incorrect values from the coolant temperature sensor when the aircon is on.

However this does sound very very unlikely to me, but it could be a possibility. Don't know a great deal about aircon specifically I'm afraid.

I suppose you could always do a further test which would be to:
- turn off car and turn off ignition
- disconnect the engine temperature sensor
- start engine
- note the revs. They might be quite high at this point.
- turn on air con
- see if revs change at all. If they do then probably this temp sensor can be ruled out as having nothing to do with anything
- turn off car, reconnect wiring

What engine do you have? Temperature sensor probably screwed into thermostat.

No need to change the thermostat, just leave that alone as your engine temperature isn't a problem.

But yes that one must be the engine temperature sensor so at least now you can try one of those tests I said about.

Good luck!

By the way, I also wish "the (wo)man who can" would come along and post "the solution" on this thread, or at least say where this idle compensator is to be found! But as yet, either no-one has any idea or they all secretly know how to fix it and are laughing at you and I with all our crazy ideas

Tomorrow I should be picking up my new S40 and I think the first thing I will do is have a very good luck around the aircon in case I see anything secretly connected to the throttle, in case it helps!!!

[COBRA31]

got my car back on sat they had downloaded some new software on to the car this at the moment has seem to have stoped the power surges did about 60miles this weekend and no promblems this might be something you want to get checked out i`ll let you now if it comes back

Thanks cobra 31 and Pete S40,
Yesterday i tried disconnecting the coolant temp sensor wire and started the car (radiator fan started turning all the while and is normal becos the wire was removed)followed by switching on the AC.The sound and responds was different.There was no sound of surging (normally the moment i switch on the AC the rpm needle will move or rev becos of the compressor came on,and there was no Bong sound coming from the compressor and the hissing sound as i described previously.Then i switched off the engine and reconnected the sensor wire,started the car again (this time the radiator fan stopped becos the wire connected) followed by switching the AC.This time i can hear the Bong and hissing sound from the compressor and you can see and feel the rpm and surge.
So i will change the sensor and try again.Hopefully this sensor is the culprit.Will keep you guys update.

Vollic

Originally Posted by COBRA31

got my car back on sat they had downloaded some new software on to the car this at the moment has seem to have stoped the power surges did about 60miles this weekend and no promblems this might be something you want to get checked out i`ll let you now if it comes back

That's great to hear some progress on this problem!

Yes try this sensor because it is quite simple to do and relatively cheap.

If it still does NOT fix the problem it would seem like the electrics / control related to how the a/c reads the signal from this sensor, or some a/c fault itself.

But lets hope this fixes it!

My advice on changing the sensor is not to bother draining any coolant off, but to do it like this:
1) Wait until coolant cold, disconnect expansion tank pressure cap to release any remaining pressure just to make sure
2) Put container under car and put some rags or plastic bags around sensor to try and stop coolant spillage going everywhere.
3) Put expansion tank back on and do it up. This will minimise coolant loss when you remove the sensor
4) Have the new one all ready, undo and remove old sensor and quickly get the new one in. You will lose coolant, but not that much. Probably less than is in the expansion tank
5) Top up, turn heater hot/cold control up to max heat, run engine until normal temperature, make sure no airlocks, overheating or leaks under pressure, all done
6) When engine warms up any spilt coolant will burn off hot places, causing smoke and smell, don't worry about that

Pete

hi pete s40 bad news.i've just changed the sensor today and is still the same.

The other time i told you that i did the test ,there was no surge becos the compressor was not activated to work after disconnecting the coolant sensor wire.Meaning i'm just getting normal blower air and not cold air.But after i reconnected the sensor wire the sound of compressor came on (the bong sound)and unusual slight rise of rpm and followed by the hissing sound(gas).Same sympthoms!after i replaced the new sensor today.
I guess we can narrow down to just the fault with the AC sys.I really feels that it's unusual to have that bong sound which sounds quite loud and the hissing sound when the AC is on.
I own a Fiat PUNTO as well and when i turn on the AC there will be a slight surge(which is normal) when the compressor comes on but no hissing/crackling sound (gas)like my volvo.
i really hope is not the fault with the compressor.it's gonna cost a bomb....

regds,
Vollic

Originally Posted by peteS40

That's great to hear some progress on this problem!

Yes try this sensor because it is quite simple to do and relatively cheap.

If it still does NOT fix the problem it would seem like the electrics / control related to how the a/c reads the signal from this sensor, or some a/c fault itself.

But lets hope this fixes it!

My advice on changing the sensor is not to bother draining any coolant off, but to do it like this:
1) Wait until coolant cold, disconnect expansion tank pressure cap to release any remaining pressure just to make sure
2) Put container under car and put some rags or plastic bags around sensor to try and stop coolant spillage going everywhere.
3) Put expansion tank back on and do it up. This will minimise coolant loss when you remove the sensor
4) Have the new one all ready, undo and remove old sensor and quickly get the new one in. You will lose coolant, but not that much. Probably less than is in the expansion tank
5) Top up, turn heater hot/cold control up to max heat, run engine until normal temperature, make sure no airlocks, overheating or leaks under pressure, all done
6) When engine warms up any spilt coolant will burn off hot places, causing smoke and smell, don't worry about that

Pete