how can i fix my 2002 renault traffic dci?

hi all. I have a 2002 Renault traffic dci. I have only had this van for just over a month, i had all the tests and a service done on the van and all was sound. I had been driving the van for 30 mins or so when it lost power, started to jump all over the road and then died! The AA came out and said his computer is not reading any fault, but guessed it was a cranksharft sensor? I was towed home ,the van was not starting,but turning over, i had a macinic come over, he started the van using carb cleaner, i said i wouldn't drive the van until the new sensor was fitted, he fitted the new sensor, the van was still driving slow but within 2 days the problem was back and i was stranded at the side of the road. this van has now had 3 different computers rigged up to it and its showing no fault, ANY IDEAS PLEASE?????

TERRY
September 2013