Puma engine trouble - help please :(

Hi,

I bought my Puma back in January this year and have had an overload of problems with it

When I first bought it the engine didn't appear to have anything wrong with it but after the first week of owning it it began hunting for revs when stationary, almost stalling when depressing the clutch at lights/coming to a stop and a limited amount of power when accelerating and suddenly bursting to life (bad explanation - oops). I've replaced the ICV and the MAF.

My boyfriend had another look tonight as changing those two things hasn't appeared to help and he said there is air coming out of the oil cap (?) when there shouldn't be. He showed me what it should be like on his car and theres a significant amount of air coming out of mine.

I'm not good at all with technical explanations but he seems to think this could be my problem. Whatever is causing that amount of air to be coming from that cap?

Sorry if that makes no sense to anyone! If you could have a go at suggesting why it might be and if you think it could be related to my engine trouble that would be fantastic.

Oh, and probably completely irrelevant but the engine can be OK one day, not too much messing around, and after its been raining hard it can be a night mare. Probably unrelated and probably in my head but just thought I would mention it.

Sorry for waffling, thanks for reading and thanks in advance for any replies!