General flashing engine management light

[dave4991]

P0300 Ignition failures recognitions
P0303 Cyl 3 ignitions failure
P0302 Cyl 2 ignitions failure

or the codes read

P0300 Ignition failures recognitions
P0304 Cyl 4 ignitions failure
P0303 Cyl 3 ignitions failure
Only ever happens when doing about 60mph (96kph)

Ive change spark plugs, coil pack and HT leads and still have the problem

Any ideas