Can anyone help by suggesting possible ignition system failure conditions that can cause the following fault codes to be generated on a 2004 VDP with approx 88,000 miles on the clock? Apparently the plugs don't need replacing until the 100K service, so maybe the plugs are not the culprit here.

Codes: P0300, P0303, P0305 and P1111.

Thanks guys, appreciate any answers that might help track down the problem.