Ford Focus 1.8 rough running

[Arran]

I have a petrol Ford Focus 1.8 year 2008.

When you start it, it runs fine for the 1st minute on idle then all of a sudden 'engine malfunction' comes up and the car goes into limp mode and the engine starts running really rough.

Im very sure it is running only on cylinders 2 and 3.

I have tried changing both plugs and coil packs from the working cylinders but no luck 1 and 4 are not doing anything?

Has anyone any ideas please?

Thanks.

[mjt]

The first port of call would be to get some diagnostic codes read. As has been said frequently elsewhere on the forum if you're handy with a Windows laptop you can save yourself a hefty bill by buying a modified ELM cable from Tunnelrat for about £20, downloading the free Forscan software and reading them yourself.