S40 (New) Engine Turbo : 1.6D 16v "Running-on"

[julianps]

2010MY 1.6D (D1614T/MTX75) - pulled out of a parking space a few days ago, moved into second gear and left my foot off the accelerator and the car rather than slowly loosing speed started to drive itself.

Noticing this increasingly and across gears that with no foot on the pedal and level ground the car holds speed, or marginally increase speed, by itself.

If I put my foot on the clutch then engine speed drops to ~800rpm; if I pull it to neutral and release the clutch it stays at ~800rpm. I know there's a neutral sensor on the MTX75 gearbox and I'm guessing there's a sensor on the clutch master cylinder as well.

As the revs fall to tick over I'm going to assume the throttle body and swirl flaps, etc are okay and the fly-by-wires accelerator pedal too.

I can only recall this happening on warmer days but that's anecdotal.

I did hear this can happen if engine oil "gets into the engine" ... and it does feel like "over-fuelling".

Does anyone have any experience or thoughts about any of this, please?

Jules

PS; there are no error messages or warning lights.

[geoffco]

Originally Posted by julianps

2010MY 1.6D (D1614T/MTX75) - pulled out of a parking space a few days ago, moved into second gear and left my foot off the accelerator and the car rather than slowly loosing speed started to drive itself.

Noticing this increasingly and across gears that with no foot on the pedal and level ground the car holds speed, or marginally increase speed, by itself.

If I put my foot on the clutch then engine speed drops to ~800rpm; if I pull it to neutral and release the clutch it stays at ~800rpm. I know there's a neutral sensor on the MTX75 gearbox and I'm guessing there's a sensor on the clutch master cylinder as well.

As the revs fall to tick over I'm going to assume the throttle body and swirl flaps, etc are okay and the fly-by-wires accelerator pedal too.

I can only recall this happening on warmer days but that's anecdotal.

I did hear this can happen if engine oil "gets into the engine" ... and it does feel like "over-fuelling".

Does anyone have any experience or thoughts about any of this, please?

Jules

PS; there are no error messages or warning lights.

If it's just driving along fairly slowly on its own rather than picking up lots of speed, I reckon it's normal... Most diesels will putter along at 'idle' revs in the lower gears as there isn't much resistance (ie not uphill) - my 2.0D certainly does in 1st of 2nd.
I think the engine oil getting past the seals / runaway engine is a more catastrophic event and would be characterised by hard acceleration and also would show an increase in the revs. Thankfully I've never experienced that so I might be wrong about it!

Geoff

[julianps]

Thanks for that; in fact there is an increase in revs.

In the car park scenario it was certainly picking up speed; where in most situations taking you foot off the gas would remove the sense of push in this car, of late, it doesn't. It still feels like its pushing on.

My neighbour's a mechanic and had an issue with a van where oil got to the engine and it was as you say quite alarming. Engine speed picked up so quickly it took speed of mind to jump in, ram it into gear and press hard on the brake to shunt-stall it (good thing there was no DMF ... ;-))

It seems a hotter day issue so I'm wondering if its an intermittent fault in the mass air, absolute pressure or whatever the DPF pressure sensor is. I was wondering too if it could be allied to the turbo but I'm not expecting much turbo activity at below 1,500 rpm.

[SonyVaio]

Yes, as above.

This is perfectly normal and the cars designed to act like that. Basically it is like an automatic choke, the engine will deliberately stop itself from stalling by increasing the fueling/revs.

Absolutely nothing to worry about.