Error P0234 - Engine Overboost Condition

[pji]

I was having some trouble with my 2003 Focus (1.8TDCi) with it stalling/cutting out when cold, which I got sorted. Seems it was a faulty sensor. The only thing is that now it stalls for a split second but not from cold, but after 5-6km. It happens two or three times and then its ok. I also feel the car is generally more sluggish than it used to be. The error code I get is:

P0234 - engine overboost condition

Any ideas? I'm off back to the garage tonight but would like to have some info from you guys first.. my mechanic mentioned possible turbo issues but he wants to have a proper look tonight.

Thanks,

Paul