Borrow or buy if reasonably cheap.
Throttle Position Sensor for C20XE. I was doing some reworking of a spare airbox and TB (opening up, thinnned spindles, etc) and decided to check the TPS and it's playing up - may be largely responsible for the flatness (leaning out) towards full throttle.
Fuel pressure regulator (or complete fuel rail) for the XE with the 2.8 Motronics - this is the later version and has slightly higher fuel pressure (3 BAR Vs 2.5) - I want to check if more fuelling will reduce the leaning out.
The reworking seems to have made a difference to the midrange, but haven't driven it enough to be sure - certainly pulling through the steering more in 2nd gear as there's slight traction loss.