Q: fiat 500x revs but wont start, has hissing noise when when to start and a little afterwards. there is also a smell of freeze spray

Depending on the hissing sound you are referring to, this may suggest you have a bit of a vacuum leak, which may be preventing the motor from starting. High idle speeds or in some cases rough idle, stalling and hissing sounds are common signs of a vacuum leak. When a vacuum leak is present in an engine, this causes an excessive imbalance in the air/fuel ratio which creates a loss of power and causes the motor to run at a much higher RPM as a result of the increased oxygen present in the fuel charge being injected into the motor. This may also be caused by an idle control valve that may be sticking or failed due to old age or deterioration. I would recommend having an expert from YourMechanic come to your location to diagnose your vacuum leak as these can be very difficult and time consuming to trace.