Customer rang to say 'glow' light on, and lack of power.
Code read the car and came up with 'P2339 CYL 4 ABOVE KNOCK THRESHOLD'

I have ran the car, and at around 1500 rpm its coughing and hunting, if I rev it hard, it seems fine.
Seriously slow to pick up on revs though.

Not sure where to go on this one, I thought maybe injectors?

Hope someone can shed some light,

Liam.