Re: Anyone seen 21 horses loose somewhere?
A very long shot, but if you have an electronic throttle the calibration may be wrong. To fix, turn your starter key over one notch, without starting the car. If your bonnet is open and you have an electronic throttle you'll hear a faint buzzing noise coming from a black box to the right of the "romeo" writing on your engine lid. Leave it to make this buzzing for a minute (it is calibrating the throttle). Then turn the key off again. Now it should have reset the throttle.
Could it also be that your exhaust is no longer airtight? Although 21bhp is a lot to lose on the exhaust.
How will you know the lambda or maf gave packet it in though? A lambda failure should give a warning light on the dash, but if it's halfway gone? I don't know.
Keep us updated as to what you find though.