following my haynes manual for fault finding, the car splutters alot over 50 mph, will splutter & backfire if i put my foot down from stand still. lacks power and over heat for a few secs if i do a constant 80 mph

I have looked for air leaks which i found on PCV Pipe? changed that, i have changed the oil + filter, fuel filter, spark plugs, ht leads, exhaust (complete) plus the lamba sensor, coolant emptied and flushed,

The spark plug wells have been filling with water which i know believe to be the core plugs which i will hopefully change tomorrow depending on the weather.

I'm out of ideas and injectors is next on the list unless you guys have other options?

Oh and it's a 2001 ford focus estate 1.6 Zetec & the engine management warning light is not on