1999 Mk IV golf starting problems

[zuegma]

Can anybody help me with this:
I have a 1999 golf 1.6 se Auto, the car starts fine in the morning and the engine runs perfectly. After the engine has warmed up, if you stop the engine and go to start it a little while later, it just cranks over and fails to start. If you leave it for about 30 minutes and try it again it still take a little bit of cranking but it does eventually start and runs smoothly.

Petrol is definitely getting through whilst cranking as you can smell it. If the car is left to rest for a few hours it starts up normally and goes through the above process again if it is needed to be restarted.

Another thing that sometimes happens when it is difficult to start, is the engine revs going up to around 2500rpm at idle. Once the car has been driven a short distance, it will go back to normal.

I would be grateful for some help and advice on this.