V50 2.4 poor idle and stalling only when hot

johna

After driving for around 10 minutes my 2006 V50 2.4i (B5244S4) will start to idle badly and then progressively get worse until it stalls if I don't hold the throttle on at idle.

I bought the car like this and was hoping to fix it easily. So far it hasn't been easy :(

It had a fuel pressure sensor code so I replaced the sensor and the code went away and the fuel pressure is now normal, but no change to the idle/stalling issue.

The PCV hose from the engine cover to the oil filter housing was broken in several places. Replaced it, no change.

It happens like clockwork, as soon as the coolant temperature gets up to ~90 degrees the problem happens and stays until the engine cools after being turned off for a reasonable amount of time. If it stalls it will restart fine and then resume the bad idle/stalling almost straight away. It drives fine when it's not idling.

I've tried heating components (throttle body, MAF, ECU and any sensors that are easily accessible) with a heat gun and trying a cold start but so far I haven't found anything. I suspected EVAP valve as I read that opens only when the car is warmed up but I disconnected it and there was no change. It is like something is switching on when the car is warm (and a second or two after restarting) that is causing this.

Has anyone had this problem or know of some system that could cause this only when warmed up or any diagnostic methods I could use?

NB. I am using a generic code reader but have ordered a DICE from China but it won't be here for a while. I've also posted this on some S40/V50 specific pages elsewhere but haven't had any success so far.

UPDATE: PROBLEM FIXED BY REPLACING THE CRANKSHAFT (RPM) SENSOR

timbo

What does it run like after you have warmed it up and let it sit for a while?

johna

timbo
What does it run like after you have warmed it up and let it sit for a while?

Do you mean if I leave it running after it is warmed up (drives fine if not idling) or if I turn it off and leave it to cool down (haven't done much experimentation about how long I have to leave it before it idles normally again)?

timbo

Mostly just wondering if it starts cleanly or runs rough on cold start eg: the next morning after driving it

johna

timbo
Mostly just wondering if it starts cleanly or runs rough on cold start eg: the next morning after driving it

Cold or hot it starts fine, never rough or hard to start. But if it is still hot it will resume bad idle/stalling after starting.

timbo

Have you cleaned the throttle body?

Can you see your short term fuel trims with your scan tool

johna

Cleaned the throttle body, yes.

This is what I was last watching on Torque while it was idling bad and almost stalling. Short term seems to be constant around 0%.

timbo

Hmm it's a weird one...nothing I can think of at the moment .

I would expect short term fuel trims to be out, and they should usually move around a bit as you rev the car up so perhaps the torque app could be pulling the long term trim data?

I have seen the PTC resistor in the breather box play up and blow fuses, they are on the same circuit as the maf sensor.

Might be worth trying with it unplugged

johna

timbo
Hmm it's a weird one...nothing I can think of at the moment .
I would expect short term fuel trims to be out, and they should usually move around a bit as you rev the car up so perhaps the torque app could be pulling the long term trim data?
I have seen the PTC resistor in the breather box play up and blow fuses, they are on the same circuit as the maf sensor.
Might be worth trying with it unplugged

Thanks @timbo ... I saw the plug on the side of the oil filter housing and wondered what it did... So the PTC resistor is used to warm up the PCV or something? I'll try disconnecting it once the problem happens and report back.

Ex850R

Id there a CTS ( coolant temp sensor ) that could be failing?

johna

Ex850R
Id there a CTS ( coolant temp sensor ) that could be failing?

There is a coolant sensor but the temperature appears to be showing correctly when monitoring with diagnostics.

timbo

Could you have possibly got a turbo rail pressure sensor as the n/a ones are different

johna

timbo
Could you have possibly got a turbo rail pressure sensor as the n/a ones are different

My FPS fault code has gone and fuel pressure is now constant (previously would go to max once the check engine light came on). From my research I have the right part for a NA and is the same part number that was in there before. But since getting that part I now have VIDA and it shows a different part number for my VIN which is a little concerning although these part numbers are listed as equivalent when I search online. The idle/stalling issue was same before and after I changed the FPS.

johna

I ran it again tonight. I couldn't find a way of reaching the electrical connector on the PCV valve without removing the airbox? Is that the only way? That might have to wait until I have some more time unfortunately.

I tried heating the cam sensor, coils and anything else in that area to see if the problem happened on a cold start, but it still took a 15 minute drive to get it to fail.

After the problem started, and it stalled a few times, on one restart it ran real rough and was idling too high but still up and down. While it was doing this the anti skid light came on and a message about anti skid system disabled or something similar. For a few starts it was still running rough like this and then on another restart it went back to its usual idle too low and stalling.

One more thing I noticed today was that once it gets hot enough for the problem to happen, if I roll down a hill in neutral it will idle fine. It's only once I come to a stop that it starts to idle bad and stall. There must be something being activated at that point that is part of the problem ???

I've got two videos if they help.

First one is a typical hot start. Sometimes it will idle bad for a few seconds and then stall, this time it just stalled after a second.

https://www.youtube.com/watch?v=5u6bNCDNo5E

Second one is a recording of this weird hot start where it ran rough and the anti-skid light/warning came on. This is not usual but it is the second time it has run like this. I left it idling on its own, but at around 1 minute I gave it a small rev to see what happened. I then turned it off and restarted and it stalled.

https://www.youtube.com/watch?v=rz33ITk_d-s

I didn't mention it in my initial post but I have cleaned the CEM connections.

carnut222

Do the throttle body motors fail in these? I assume that's what controls the idle speed, not like the older cars that had a separate idle speed air bypass valve? Hmm....

johna

carnut222
Do the throttle body motors fail in these? I assume that's what controls the idle speed, not like the older cars that had a separate idle speed air bypass valve? Hmm....

They do have an electronic throttle body and they are problematic but I've tried to eliminate this as the cause (although I'm far from 100% sure).

carnut222

Just watched the videos. Very strange...especially that anti-skid message. I wonder if it has something to do with a speed sensor of some sort? Could it be telling the engine to cut power because it's detecting wheel spin that doesn't actually exist? Maybe have a close look at all the wheel speed sensor wires to make sure there's no frayed wires, poor connections etc? Just a theory - if it's somehow linked to the traction control...

johna

carnut222
Just watched the videos. Very strange...especially that anti-skid message. I wonder if it has something to do with a speed sensor of some sort? Could it be telling the engine to cut power because it's detecting wheel spin that doesn't actually exist? Maybe have a close look at all the wheel speed sensor wires to make sure there's no frayed wires, poor connections etc? Just a theory - if it's somehow linked to the traction control...

Thanks. I will check into speed sensors and see what connection there might be with idling to the anti-skid system.

timbo

I have never seen any issues with the throttle bodies on these cars.

The only "speed sensor" the engine really cares about is the crank sensor

None of the abs sensors usually give any trouble but the front hubs can cause wheel speed sensor faults. This was Volvo's fix

https://blog.fcpeuro.com/how-to-install-a-volvo-wheel-bearing-lock-brace-p1

johna

My other car, a BMW, has a visible difference when it is moving and idling as opposed to stopped and idling. The revs are about 200 higher when rolling in neutral. Then when you stop the revs come down to the normal idle speed. I was thinking the Volvo might do something similar - it is certainly idling different when moving than stopped.

I looked at that link but am thinking that it might not be my problem because my car simultaneously threw the ABS error and started idling very rough while it was sitting still. Electrical problem I wonder?

I'm thinking I need to wait for my VIDA diagnostics hardware to arrive before I am going to be able to sort this out. Hopefully there are some better clues in fault codes that aren't shown on the regular OBD scanner I have now.