Intermittend power loss

Power loss seems to be a general complaint. My 2002 TD5 manual occasionally feels like the turbo is not spooling at all. This happens after switching the engine off for about 15 to 20 minutes. After 2km or so it is ok again. I have replaced the actuator. This engine was redone by the previous owner, injectors as well. Where do I start? Being intermittend it is difficult to find the problem. Will the engine run properly if the injectors were replaced but the new codes not punched into the ECU?

the codes are quite important to be programmed

any oil in the ECM red plug? ... if not replace the wastegate modulator to rule it out unless you have access to tester

Modulator- regulator, is that the same thing? I replaced the unit with the 3 pipes and electrical connection.
My question is will the engine run without the correct codes for the injectors on the ECU or will it just be confused by overfueling some and underfueling others? I am loathe to take of the tappet cover without having a new rubber gasket/packing.