I had an emissions failure last month, after doing everything you have mentioned I decided it needed to go to a 'Specialist'.
It transpired that it was a bad ground to the first 02 (Lambda) Sensor which I would never have found.
A temporary earth (Ground) was spliced into the Sensors wiring and it flew through it's Emissions test.
Basically I was getting a 0170 coded fault which pointed towards the 02 Sensor.
0170 - Fuel trim Bank 1.
Then after cleaning and swapping bits it developed into '02 Sensor Circuit Fault' (Can't remember exact wording or code).
I must have damaged the wiring loom during my cleaning phase.
I experienced the same as you described (loss of power if anything more than 50% throttle) but only got 0170 code on it's own.
It also had a very slight 'Miss-fire' which wasn't a miss-fire but unspent fuel burning in the exhaust due to ECU running engine rich to compensate for the 02 Sensor not being active (broken earth).
I have also had issues with power and starting when my Fuel pump started to fail. This was also linked to a failing Fuel pressure regulator (located on fuel rail).
What was happening was the pump couldn't supply enough fuel beyond 50% throttle and there was only 2.4 Bar at the rail.
I believe the 2.2l 16v requires a minimum of 3.0 Bar of pressure.
Now the pressure regulator has a small pipe running to the throttle body which creates a vacuum for the regulator which could also create a fueling issue if it has become faulty (i.e. Taking too much pressure from the fuel rail).
Obviously both the pump and the regulator work in unison so it is necessary for both to be working correctly.
May I suggest a pressure test on your fuel rail and a full diagnostics being done.
This cost me £75.00 inc VAT to find the problem which I would never have found myself.
Hope this helps
