Dificulties with the warm start. Any opinion?

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When I start the car in the morning it starts ok. After I drive the car and stop it for a short time is also starting without any issue. The problem is if I leave the car for 1,2 or 3 hours and I try to start it. Most of the time it will start and then it will stop after 1 second and I need to keep the starter running for a long time before it starts again and after it starts it will run just with few cylinders only. It helps if I keep the throttle pressed a bit but still too dificult. . I noticed lately that the idling looks to be ratling when engine is hot. I live in Dubai so it's hot weather. Any sugestion? Also an advice regarding the heat range of the spark plugs? Thanks