2012 508 2.0HDi High Idle

[RobTy]

Hi all,
All advise appreciated on this issue. I have a 2012 2.0 hdi 163bhp that when fully warmed up will sit with a high idle of around 1300RPM. This reduces to normal idle (800rpm) when the brake pedal is pressed but goes back to 1300rpm when released. It will also drive at this rpm when the accelerator pedal is not pressed i.e. 50mph in 6th gear.

I have ran a standard diagnostic tool on it and it showed a faulting O2 sensor which I replaced but the issue still remains, I have checked and cleaned all other sensors (air mass, boost pressure, etc,) & connections.

Right now I am stumped.

Thanks in advance for any responses.

Rob.

[myglaren]

My initial thought is an air leak in the brake hoses or the master cylinder.

[RobTy]

My initial thought is an air leak in the brake hoses or the master cylinder.

Thanks myglaren,
I thought the same and checked the air line from the brake servo, can't see any leak. It's only a short one (about 2 feet long and goes to the side of the head).

[RichardW]

Surprised there isn't a code and / or engine management light. This is a default strategy if input is lost / confused from one of the sensors - e.g the throttle position. You need to get some live data and check all the sensor inputs, looking for one that doesn't make sense.

[RobTy]

Surprised there isn't a code and / or engine management light. This is a default strategy if input is lost / confused from one of the sensors - e.g the throttle position. You need to get some live data and check all the sensor inputs, looking for one that doesn't make sense.

Thanks Richard,
I'll check out the live data.

Rob.

[RobTy]

Hi all,
I have had an interesting investigation outcome on this. There was no engine light or service light on. I hooked it up to a "decent" code reader and hey presto, P0272 - cylinder 4 contribution imbalance ". Removed top engine cover to inspect injector and loom and was greeted by a sea of hardened carbon deposits. Almost unable to see cylinder 4 injector.
Seems the injector seal is leaking letting compression with unburnt carbon passed it. An hour later of cleaning you can see the injector. With it running, very roughly may I add you can feel the cylinder compression with your hand at the side of the injector.

So, next step is to keep cleaning, remove and replace injector and all the burnt loom and connections along the way as well as whatever else decides to crumble in my hand. It must of gotten hot under there.

Will keep you posted.



Rob

[Jodypug]

Did you find a fix to this please?

Mine is doing exactly the same but tried a couple of garages and they have no idea and I can’t find any answers online