Focus Rough Idle And Power Loss.

Hi there, just bought a 2003 Ford Focus MP3, the car has a rough idle and stalls sometimes when started, sometimes it will rev up to 1200rpm and recover itself and other times it won't. It seems to be more prone to stall when under load (when I have the lights and fans on). It also seems underpowered (my 1.2 corsa c seems to accelerate faster). I have already cleaned the Idle control valve to little avail, replaced the air filter (which discovered a new problem - oil in there, probably over pressurising, im yet to do a compression test) and cleaned the MAF.

I've ordered a new ICV and will replace tonight, if that makes no difference am I right in thinking it could be the throttle position sensor, coil pack or even lambda sensor? I don't know how I would test these without simply replacing them either? Any help would be really appreciated!