1999 Renault Clio car never starts up first time and revs never stay constant when idle

some days i can start my car up and its absolutely fine. However 80% of the time when i start it up it takes at least 3 attempts for it to start and i also have to put my foot on the gas pedal to give it that extra kick. Also when im in traffic or even if i just put the car in neutral, the revs will start going up and down and sometimes drop as low as 500 and i can feel the car about to cut out. I thought maybe its the car dying out on me as its done a lot of miles (118k).
Any ideas?