I love my Skoda like crazy. 1.9 TDI, BSW engine, 258K km on the clock, well-maintained from the first day, only OEM filters, Motul-specific oil etc.
For a long time, I have felt power loss and bad consumption—6.5 liters/100 kilometers at its best.

Turbo works fine and can hear it, Pulls from 1600~ rpm but not like a tractor like it used to be.
Deleted EGR and fitted N75 valve instead of vacuum box - NO CHANGE.
New fuel filter - NO CHANGE

NO CODES on the computer

Back in time, I could reach 200 kilometers per hour, now I'm barely getting to 150~.

The engine starts and works perfectly. 

 

Once a month or two, suddenly the car gets its power back and it could be felt, after a few minutes it loses it all .

ANY IDEAS WHAT TO CHECK? ANY POSSIBLE WAY TO FIX?

 

Thank you!
 

Had a simular fault on my old MK2 1.9, never showed any faults but as you said power would be down with no logical reason, went through normal steps but nothng seemed to respond,, then one day the engine light came on and fault showed up as turbo  overpressure so ecu went into limp mode but then came out but performance still not right, it turned out to be a faulty  actuator on the turbo and  was slightly sticking and although turbo was boosting it ws was not enough, i bought a new actuator from   the bay £50 odd fitted it  and the cars full power returned back to normal, I also changed the top and bottom rubber boost pipes to the intercooler as they looked a bit scraggy