Hi the problem is power loss

The symptoms:

Car was fine for 1.5 Km then I stopped and was on tick over for a few minuits then pulled off and it seemed the turbo was not working so I drove off and manage to get about 1 Km where I stopped and checked the engine visually and found no problems.

I started the car and noticed that the power loss was getting worse and gradually worse to eventually the van would not rev over 1500 revs but tick over was perfect No engine lights have come on Its now been in the garage for 2 days and they do not know what is wrong They have used a lap top to check the car and found no error codes They have checked the turbo and thats fine They have checked various other things but still no luck please help