Hi - even though you've blanked the EGR (its a solid plate? - no holes to let the gasses through?) the inlet manifold could still be "coked up" from 10 years of carbon/ mock + the breather muck adds to this forming an oily sludge

so your engine may be getting "choked" from this carbon/ sludge

an older engine may produce a lot of muck from the breather - you may have to clean out the intercooler too - and fit a catch tank to the breather outlet
You don't mention whether you have changed your air filter/ when was it last changed - again - this can choke/ restrict your engine

the injectors on a TDDI are mechanical and do not need to be coded/ recoded - they have a reputation for being more reliable/ doing higher milages than electronic injectors (TDCIs)

does your car have a fixed vane turbo with wastegate and actuator or a variable vane turbo?, (the variable vanes can coke up/ sieze)

the turbo relies on energy from the engine, if the engine is not producing the heat/ pressure energy to "feed" the turbo, (eg - if it is choked or has a fault) the turbo will not boost up, causing a "knock-on effect"

A fresh air filter is under a tenner and cleaning out the inlet manifold should be cheap too - always best to do the cheaper things 1st, especially if they are "sevice" items too (or should be)