P38 Diesel Engine revving on cold start

Does anyone have any idea what causes my p38 diesel to rev at approx 2000 revs on cold start? (I'm only guessing as the rev counter does not work when this happens). This is only at this time of year, so is obviously temperature sensitive. It also locks the ride height and this goes onto the stops. After a time it runs in normal mode and everything works perfectly. All the heater plugs work ok and the light comes on and then goes out before starting. Any suggestions? My son suggested a match! I hope he was only joking.

it will be the crank sensor it is either knackered or needs adjusting in a bit but be carefull as you can knock the end off it,when yours is running normally just pull the plug off and you will get the same symptoms 2000rpm and no rev counter

Many thanks. I will give it a go when I get it in our workshop.