Zafira 2.0dti 2004 loss of boost since driving in flood water?

I drove the car through 1-2 foot of water yesterday. The car made it through but juddered a little. Since then I have had a loss of power (like limp mode), but i have no warning lights on the dash. I have checked the oil for contamination and was fine, I have checked the air filter which did have some water in the tray. The car starts ok and ticks over fine and there is no abnormal noises etc. It drives ok apart from the lack of power which notices more going up hill and only doing 70mph on the motorway with foot flat on the floor. What could be the problem?

Brett
August 2013