My 323F automatic - pop up lights- has a horrid problem.

When engine cold it starts well, if it misses then it will not start for at least 10 minutes.
When started it starts hunting and nearly stalls. If i do a short journey, about 10-15 mins, then it will not restart for at least 30 mins. On the motorway and after a long journey it is fine.

Changed the air meter, throttle box cleaned. Mazda dealers stumped.
I was thinking lambda or water temp sensors.

Does any one know a good place to get these at non-mazda prices