Occasional misfires

[Crofty1984]

Hi all, 
I have a 2007 1.6 HDI berlingo multispace, with an odd fault.
Normally it starts, runs, accelerates, cruises perfectly well, but very occasionally it'll stutter, just once like it's misfired, then back to normal driving again. It seems to be worse when cold and at very light throttle openings, like at 50 in 5th gear in the mornings. Sometimes it'll go a week without doing it, other times it'll have this little hiccup 2-3 times on a journey. I've serviced it with new oil air and fuel filters and also chucked a couple of bottles of redex injector cleaner through it. I did think it was maybe pulling in a little bubble of air from the fuel filter change but it seems to have been happening too long to be that.
I've scanned it and got codes P1350 and P1351 but they throw up various possible causes depending on manufacturer and Citroen doesn't feature.
My next thoughts were either a sticky injector or maybe TPS, but who knows?
Any advice appreciated.
Thanks,
Dan

[Sol]

Most likely in my mind, would be the MAF sensor. Try unplugging it and see how it runs. If it is flawless without it then replace the MAF with a new one. (cleaning will usually not help - but you can try it)

Those codes are for glow plug issues and may be historical (the HDi doesn't need glow plugs to start, except in very cold temperatures) - the official Citroen descriptions are:

P1350 Pre-heating relay circuit : Control short-circuited to earth or open circuit
P1351 Pre-heating relay circuit : Coherence ; Relay supplied and glow plugs not supplied