Please help :(

My wifes 97 galaxy 2.3 petrol engine. She said it felt under powered and was almost felt like it was mis firing.

I started the car this morning and revved it, a huge amount of smoke came out slightly blue in colour and the car didn't sound smooth and like it was mis-firing. I drove it to work and bellow 3k revs its really struggling above 3k its better but not right, it wasn't smoking that much that I could see but seemed to use a lot of fuel. Checked the air filter all seemed clear and tried the car with air box off and no different, I knew the spark plugs weren't brilliant so I got some at lunchtime and they were pretty poor, fitted the new ones. Car was slightly better but not much, still missing and it smelt like a lot of fuel not being burnt out of the exhaust.

Any ideas on what the problem could be or what to check next?

Thanks.