After a few hours messing with it, finally found a solution to that problem which created a new problem. I'm starting to get frustrated now. I ended up going all out with the car, drifting around and doing a few burnouts ( not too hard ) which caused the car to start working properly again, RPMs dropped but around 50-100 at maximum and rarely, which is normal. I reckon it was one of the spark plugs which wasn't working, causing it to pop, misfire and have a struggle with running.
New problem - Car tends to overheat when idling on spot. It almost caught on fire, I freaked out. I went into the garage and left the car cooling down after 3 cooling laps infront of the garage, came back outside in like three minutes and there was smoke everywhere, the coolant was boiling and the green coolant liquid was all over the engine bay. Only way to cool it down was by driving - what could cause this?