Delay start happening in Toyota Vios Car

[sanda]

Hi All,
This issue was happening When starting the engine, starter motor kicks in about 2 or 3 times to start the engine. When i turn off the engine and starts the engine within 2 to 3 minutes, it starts instantly. But when I keep it for around 10 - 15 minutes or more time as I previously explained delayed starts occurs.this issue was been going for a year.

I did few things to solve the issue at past but that issue was not fix permanently and it only work for a maximum 3 to 4 month then it is again happened,so what i did

1.Engine tune up done but no any improvement 

2.Start mortar repair but no any improvement  
3.fuel pump replaced(within 1 year 3 times replaced)issue was fixed only 2 times and again came after 3 to 4 months.

4.finally change fuel pressure regulator (issue was fixed and again came after 3 to 4 month)

5.last time on today also I changed fuel pump with car technician then no any improvement, at the moment i have to kick switch 3 times to start the engine so i can see very hard to start

In my car there are no any issues and all are working fine, services also done at the correct time.Could any one suggest what will do on next level 

Thanks