[Britwrench]

Take the ignition wires off the plugs and check for water left around the plugs. Also make sure the fuel pump relay is new.

You might also want to check the fuel pressure as too high pressure, due to fuel regulator failure, can cause similar problems although usually it's so bad the engine won't run.

There are a number of faults that can cause the problem you have, you are going to have to do some proper logical diagnosis. Hope you have a workshop manual.