dodgy idle and start up

[Dec_blue_vtr]

hi there. basically when my car is running at idle, sitting still every now and again it revs itself up to 2000 then drops back to 1000. and now when i try and start it i could turn the key and it not want to start then turn it off then back on again and it will start, but when it starts it either runs normal or asif it wants to cut out but doesnt and after a minute or to it will run normal. Any ideas of what it might be or what to check would be brilliant.
My car is a 1999 vtr with a completely standard engine.
Thanks

[Lewis]

Coolant needs bleeding. Otherwise ICV problems

[dt_]

temp sensor, located on the right hand side of the block, about £10

[reverend_jt]

ive got a '98 vtr. it did the same until i flushed my radiator/refilled the coolant. I also got a new thermostat. cost £8.99 for the thermo plus a fresh bottle of coolant.