Vauxhall Astra 1.6 Sport R reg 97. Intermitant Fault.. Any help?

My Astra has been playing up for the past couple of weeks - It started to overheat after 5 mins when the engine was freezing cold as had been left all night, steam was coming from the coolant, heat inside the car stopped working. A few hours later car was fine, it does have oil, water and anti freeze! Was told this was an airlock.

A few days later the car is Reving up to 5000rpm on its own when driving, and holding itself at 2500 when starting. its cut out a few times and feels like it will stall,theres a loss of power, and the engine light has been popping on every now and again. If stopped with engine on for more than a couple of mins the tempreture flies to the red on the gauge, then the fan cools it down but this never used to happen this quickly before!

The EGR Vowel was changed less than18 months ago so not convinced it would be that, aswell as everything is pretty new except the engine its self - have already plugged it into Diagnostics but no fault showing at all.

Any ideas Please!!???