V40 1.8 Intermittent stumble and rough idle

[scinoz]

When I start the car it idles for about 10 seconds and then I hear a noise (sounds almost like the air con compressor kicking on -- but its not). When the noise happens the engine runs very rough. After a period it makes another noise and the engine smooths out.
Then when driving, the engine stumbles from a standstill -- but is fine once the revs get up.

I've changed the coils, plugs, plug wires, cleaned injectors -- still happens.

Any Ideas?