Could be a few thing mate
Oxygen Sensors
PCV Valve
Coil Pack (non-turbo)
Coil Packs (for turboed cars)
Spark Plugs
Spark Plug Wires
Dirty Injectors
Dirty Throttle Body
Dirty Electrical contacts on MAF or MAP sensors (Simply use Electric contact cleaner on the contacts. Do any you can find really, it's not bad for them.)
Dirty or failing MAF or MAP sensors
Blocked, Clogged, or 'on its way to failing' Catalytic Converter
Coolant temperature sensor