2.0 HDI Losing Power

[gogantus123]

Hi all,
I bought a Citroen Grand C4 Picasso 2008 year 2.0 HDI 136hp automatic 6sp about a year ago.
The car has been driving perfectly and I noticed that the car feels very slow (like it has 90hp), but sometimes out of nowhere the car starts driving as it should with all the 136hp.
When the car feels like 90hp, it shifts gears slowly and it is very slow. And then, out of nowhere the car feels very fast that even when accelerating from stationary the tires start chirping, and the car gets up and goes.
I don't think someone did a remap to the car or something, and when feeling that 90hp the car idles normally and there are no light's on the dash.
I've heard that it could be due to a filter, but I changed all the filters and the issue still persists.
I've also head that there are vacuum pumps which fail, but I don't know how to test them.

Does anyone have any ideas what I should check?

[toolfan]

I had a similar issue on my C5 2.0 HDI 2007. I found out that the turbo was always on the "wide open" position due to a failure of the electro-vacuum solenoid which regulates the variable turbo geometry. You also need to check the vacum hoses and connections for damage and loss of vacum. If you have a vacum tester you can check if the turbo vanes it self are mooving. Three possible issues concerned with vacum.

[penners11]

There are 3 electro-vacuum valves, 2 fixed on the air con pump, as you say, check all hoses with a vacuum pump, my fault was hidden behind the y junction on the intake pipe, the r/h side controls the air volume butterfly/turbo boost, a 90° elbow had perished and come of a vacuum collector. 2.5 cm of 4.5 hose fixed it. Frustrating or what. Once your sure the pipes are OK, you can check the electro valves with Lexcia.