As above really guys...
It's a 2000 W reg Focus, 2.0 16v - which feels more like a 1.4!!! Seems to be holding back!!!
Has been driving ok, feeling fine, other than low on power - idle is good, always starts first time, etc...
However, it has now started to misfire - but only at full throttle!!! Pretty much any revs, put your foot to the floor and it really struggles - no acceleration at all until you back off to maybe 80% throttle, where it drives fine again!!!
Doesn't seem to do it when standing (no load) and revs fine at full throttle then - just struggles under load!!!
I did find a couple of plug leads that didn't seem to be on all the way so I re-seated those properly.
Also found a small earth lead to the top of the engine which had broken off, so I've fixed that.
No difference at all after those two bits - so where do I go from here???
Could it just be dodgy plugs, or something more???
Any help greatly appreciated!!!