940 LPT Idle Woes... Help!

[LPTJoe]

UPDATE: I have removed and thoroughly cleaned the ICV with throttle-body cleaner, no improvement

The issue only seems to effect the car during warm up with idle surging occasionally to 2000rpm+ and holding there for a few seconds without the throttle being used, before crashing back down to 500rpm or so. The car actually stalled this morning when coming back down from a surge...

Once up to temp the idle holds at a steady 700-900rpm without any serious hunting.

This seems to be very much temperature related with all pretty much ok once up to operating temp. Surely if it was MAF/leaky hose related it would present at all times? Do these car's have an automtic choke? Something on the cold running circuit is causing this for sure IMO.

At the weekend I will change coolant/temp sensor/thermostat as I believe the CTS could cause my issue given it only seems to happen when cold/warming up...

[Laird Scooby]

Originally Posted by LPTJoe

UPDATE: I have removed and thoroughly cleaned the ICV with throttle-body cleaner, no improvement

The issue only seems to effect the car during warm up with idle surging occasionally to 2000rpm+ and holding there for a few seconds without the throttle being used, before crashing back down to 500rpm or so. The car actually stalled this morning when coming back down from a surge...

Once up to temp the idle holds at a steady 700-900rpm without any serious hunting.

This seems to be very much temperature related with all pretty much ok once up to operating temp. Surely if it was MAF/leaky hose related it would present at all times? Do these car's have an automtic choke? Something on the cold running circuit is causing this for sure IMO.

At the weekend I will change coolant/temp sensor/thermostat as I believe the CTS could cause my issue given it only seems to happen when cold/warming up...

Have you checked your coolant level lately? Try topping up the expansion tank to the brim and giving it a drive.

[LPTJoe]

Yes.

coolant tank is full to the max markings.

[TonyS9]

I think 2000rpm is way high, but that the ECU has decided to open up the ICV to compensate for AC or Auto drive select.

I presume this is a manual car, does it have AC?

I have no idea where those connectors might be, but we might be able to determine the wire colours or, better, pin numbers. Then you will need to remove the kick panel and perhaps the ECU and perform surgery to find and cut the wire and connect them to the multispade ground nearby. You may also have to cut the security screw to release the ECU.

Actually tbh its sounds very like the problem I still have with my 360 (97 B230FT), which I think is throttle body related. It quite often happens if I rake it or rev it hard when its cold. I'm fairly certain I have grounded the concerning inputs. It doesn't stall though, and usually returns to normal if not moving (cold running increases rpm at certain temps until stop moving), however the other day it did seem to get the high rpm thing after a long run (during which I may have gunned it), only reset by engine off/on.

[LPTJoe]

Originally Posted by TonyS9

I think 2000rpm is way high, but that the ECU has decided to open up the ICV to compensate for AC or Auto drive select.

I presume this is a manual car, does it have AC?

I have no idea where those connectors might be, but we might be able to determine the wire colours or, better, pin numbers. Then you will need to remove the kick panel and perhaps the ECU and perform surgery to find and cut the wire and connect them to the multispade ground nearby. You may also have to cut the security screw to release the ECU.

The car is manual and doesn't have AC.

Thoughts and prayers are focused on it being the CTS at this stage rather than the actual ECU that's at fault...

As I say, it has to be a temperature related issue as it's only happens for the first 10 mins of running, once warmed up the hunting all but stops...

[Laird Scooby]

Originally Posted by LPTJoe

As I say, it has to be a temperature related issue as it's only happens for the first 10 mins of running, once warmed up the hunting all but stops...

That was why i asked about the coolant level - on some cars i've owned, a slightly low coolant level can cause exactly the problem you've got.

What's your electronic knowledge like? If i can find the values for the resistor needed to temporarily "dummy" the CTS it might give you confirmation one way or another but do you have or could you get quickly the right resistor if i told you the value and would you be ok fitting it temporarily?

[LPTJoe]

Originally Posted by Laird Scooby

What's your electronic knowledge like? If i can find the values for the resistor needed to temporarily "dummy" the CTS it might give you confirmation one way or another but do you have or could you get quickly the right resistor if i told you the value and would you be ok fitting it temporarily?

Could do, but given I've got a new CTS to hand probably easier just to try a new sensor I recon.

[LPTJoe]

UPDATE: Having just driven home from work I've now got the lambda/emissions warning (Green triangle/orange background)

I've got three different OBD2 readers, the car has a port under the armrest and yet none of them will speak to it.... FML

Not sure where to go next TBH.

[Laird Scooby]

Originally Posted by LPTJoe

UPDATE: Having just driven home from work I've now got the lambda/emissions warning (Green triangle/orange background)

I've got three different OBD2 readers, the car has a port under the armrest and yet none of them will speak to it.... FML

Not sure where to go next TBH.

You've got the engine management light on and the reason your OBD-II readers won't work is because it's not an OBD-II port.

It's Volvos attempt at it and needs Volvos own reader although some people have built their own using an LED and resistor - i believe the instructions and fault code tables are in the FAQ somewhere.

That's really your next port of call - check the FAQ for that fault code reader, build or borrow one and read the codes.

Until you do that you're basically shooting in the dark.

You could try fitting your new CTS and pulling fuse #1 (i think it's #1) for a few minutes to reset the fault codes, see if that does the trick.

If not then it's all down to whatever codes you can pull.

[LPTJoe]

Originally Posted by Laird Scooby

You could try fitting your new CTS and pulling fuse #1 (i think it's #1) for a few minutes to reset the fault codes, see if that does the trick.

Thanks.

Will disconnecting the battery for an hour or so not clear the codes?