[RogerHeinz57]

Be under no illusion - "Guess-nostics" will be costly !
As stated a suggestion of cam sensor proves beyond doubt the guessing is pointless !
So let us attempt to encourage you with a more viable set of suggestions - based on very little information provided.
Have you had this vehicle plugged into a fault code reader / T4 or on to a suitable machine, any live data to provide ?
In fairness, there are a couple of main areas of weakness with this engine and worth a few checks or experiments after thinking about how well maintained the car is histrorically. The MAF sensor is a regular culpret as this item makes calculations for fuel to air ratios to send to the ECU, this takes measurements of air density/pressure. If this component has run it's lifespan and is out of range, there will be various fuelling issues which will include quite boring performance from the engine generally. The MAF sensor can be disconnected, this will inspire base / default information which allows a level of operation, and may allow better running, but not totally ideal for all engine speeds/loads.
That is one of the few sensors that may be misbehaving, but clearly the easiest to try out, and I would advise insulating the connector plug when removed inside a plastic bag and sealing it as best you can.

So this would be one of the areas to check early on, there are other subjects to check, intercooler hose for leaks, under-bonnet fuel pump leaks, fuel filter leaks, a very noisey under-bonnet pump may well be one that is at the end of it's service life and just hangining on by a thread. These are a few areas to check, and I am sure there will be a number of guys on here who may advise you on what your findings are should you share them here.