When I stopped my car just now, I turned the key and removed it, the engine stayed on for 2-3 seconds and then shut off. Never done this before and I tried restarting and shutting off again and it didn't repeat itself. 

Could this just be a freak thing, or is this a sign of something serious?

Usually carbon build-up glowing red hot in the combustion chambers cause this.

 

Do you drive sedately?

We do mostly, is it worth me giving it a good blast?

That was once true on petrol engines with carburettors but the fuel will always be shut off on a diesel and in any case diesel does not need an ignition source like the carbon quoted, maybe some dribbling from the injectors on a previous generation engine but not from a PD diesel.

 

Something is maintaining the pulses to the injectors or one or more is not sealing off properly, I will have a read of my PD study guide later.

The switches in the ignition may have just got stuck momentarily, I agree with JR in that the issue is not likely to be mechanical.

 

 

Well it hasn't done it before and it hasn't done it since! Rear wiper motor has failed now... Great!

Anti shudder valve sticky and needing cleaned.

8 hours ago, MicMac said:

Anti shudder valve sticky and needing cleaned.

Is that another suggestion as to why it stayed running? I'll keep an eye on whether it does it again. 

1 hour ago, gman88667733 said:

Is that another suggestion as to why it stayed running? I'll keep an eye on whether it does it again. 

Yes.

Can the carbon build up be burnt off by a really good blast at high revs, or does it need to be taken apart and cleaned?

Another thing is always watch for your oil level rising.  Diesel in the engine oil.

A diesel engine running on and not being able to stop is a scary thing.

Okay, I'll check the oil every day for the time being. Still hasn't happened again since, been in and out with in quite a few times. 

I've been driving around in S mode on the gearbox, which is actually rather fun!!

Is it regenerating as ours does it quite often, as said it is burning off soot etc.Skoda say it is quite normal BUT before the update on emissions it did not come on.

My Octavia does not have a DPF. It's a 2005 model

16 hours ago, gman88667733 said:

Rear wiper motor has failed now... Great!

 

You've done well, 13 years is roughly 12 more years longer than they usually last.

37 minutes ago, silver1011 said:

 

You've done well, 13 years is roughly 12 more years longer than they usually last.

Well that's something! 

Seems to be working again today, and the horrible dry bearing sound has gone.

I think it is caused by the rear wash not really working properly because the washer jet keeps getting bunged up. Without the jet in, the washer works properly.

Be careful, the Octavia is well known to pop off any one of a number of weak plastic tube connectors along the washer fluids route from the engine bay to the rear screen.

 

Prolonged use of the pump with the nozzle bunged up (or the washer fluid frozen) usually result in a boot full of washer fluid.

 

If you have the appetite or enthusiasm, opening up the rear wiper motor and applying copious amounts of grease can often prolong its use for another few years.

I'll give that a go. Is it worth taking off all of the boot trim to see if any water has leaked down? Also, how can I check the pipes are all connected securely?

10 hours ago, gman88667733 said:

Is that another suggestion as to why it stayed running? I'll keep an eye on whether it does it again. 

 

The ASV is not solely responsible for stopping the engine running, it airlocks the engine in order to stop it quickly but only after the Injectors stop. As the name suggests the engine would have 'shuddered' to a stop rather than stopped cleanly which you would have felt and heard.

 

Also the ASV Is stepper motor controlled on your engine and is part of the EGR system so they usually throw a code if they malfunction so scanning the car for codes is another way to prove it.

 

 

The car shut off without any extra shudders or noises really...