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The car has started playing up a bit (how dare it after 4 years trouble free motoring),anyway on occasion when i turn the engine off it will sometimes "run on" for a second or so and then the mfd throws up "anti pollution fault". I have a basic code reader/reset thingy and it shows fault code "P0090",i have searched the net and would i be correct in thinking it is a fuel pressure regulator fault? The car doesn't go into limp mode and drives just as it ever did just sometimes runs on.Any info greatly appreciated.

It is a generic fuel pressure regulator fault code, but could just be misleading. If you turn the key off & the engine doesn't stop, it will have about 300 bar fuel pressure more than the ecu's expecting to see......

The real question is why doesn't it stop? Any chance you've got a dicky ignition switch and it's 'bouncing' between off & on enough to confuse the ecu?
Maybe you could prove it by pulling a fuse to stop the engine.

When i say it doesn't stop it sort of stumbles to a stop after the key is switched off but it is only for about a second or so,i too thought about the ignition switch in the first instance.In my understanding with the common rail type engine the injectors are operated electronically so lets say the fuel regulator was not shutting off the fuel when you killed the ignition the car should still not "run on" as the injectors should be shut as there is no power to them? so even for the engine "run on" even momentarily with the ignition off there must be power to the injectors?

According to Steve @ HDI tuning this is a very common problem on these.
99% of the time is cured by removing the pressure sensor on the HP pump & giving it a thorough clean up.
Use carb cleaner & blow it out with an airline, just be careful of the o-rings on the sensor

Cheers for the reply,do you mean the pressure regulator? I was thinking of getting one of these? http://www.ebay.co.uk/itm/271932777814? ... EBIDX%3AIT

Yes, & that'll do nicely

I'd better start soaking the torx bolts that hold it to the HP pump as it looks a bit of a rusty mess.

Mine came undone quite easily, but I bought my replacement seals/washer from Peugeot - I should have checked eBay first.
The only thing I would suggest is that if the regulator doesn't want to come out with a gentle tap, then leave it be - don't risk breaking the tip off in the pump.
You can undo the 2 10mm bolts that hold the fuel filter housing and flip it upside the out of the way, even the pipes can stay connected...

I have had this fault (and several others) caused by the regulator on the HP pump, I actually changed it for poor starting when hot but it also cured the 'running on'.

I didn't have any difficulty getting mine out, it has a 'O' ring on it that can make it appear to stick but it came out without to much effort.

Peter

There's a useful video on you tube showing tips on removal