I'm at the "the injectors are the prime suspects" stage too. I've got an oil and fuel filter service in about 8000km and I've already been on the horn with the dealership about the weak power problem.
They said they can analyse the fuel to air ratio and make sure it's within trim values. Could be that the timing needs readjustment and/or the injectors are fouled preventing the proper quantity of fuel entering the cylinder. That would manifest as a loss of power/flat spot/hesitation I would think.
I've tried a bottle of injector cleaner in the gas tank, but it didn't really do anything so I'm going to have the dealer hook it up to their computer and see what comes out.
Don't know when the appointment will be but probably around end March/early April. I'll have them change out the winter tires at the same time.
On the peugeot forums a couple of guys have had success by removing the intercooler and draining the oil and flushing it with degreaser. I think it's a bit of a job to get the intercooler out, however.
Did they look at the turbo vacuum solenoid that controls the variable vane geometry? I think the solenoid is down under the fuel filter somewhere around the EGR if I'm not mistaken.
Maybe oxygen sensor?
I mean loss of power on a diesel is due to one of two things: (1.) poor Airflow or (2.) poor fuel flow.
Right still got the flat spot between 1000-2000 rpm hard to replicate but happens when you put oof down from cruising say.
Today I took egr valve off cleaned it all out and the heater part and entrance to engine block.bolted all back together took for drive and till there so far I've done
Dpf delete +remap
New charge pipe from intercooler
New air filter
Bmw had car for a week and couldn't find anything
Where next to look? Injectors?