Engine Delayed Start - Toyota 1NZ-FE 1.5L

[SL Runner]

Dear Experts,

I'm a victim of using contaminated petrol. Experienced engine missing at 1000RPM and later on, cleaned injectors using BG Injector cleaner. Thereafter engine missing issue was resolved. But I started experiencing engine delayed start.

Vehicle: Toyota IST - 2008 - 1NZ-FE 1.5L engine

Description:

When starting the engine, starter motor kicks in about 2 seconds to start the engine. When you turn off the engine and starts the engine within 2 - 3 minutes, it starts instantly. But when you keep it for around 5 - 10 minutes, previously explained delayed starts occurs.

What I did so far:

I took my vehicle to Toyota and they checked the fuel line pressure and said there is a pressure drop. So they advised me to replace the fuel pressure regulator in the fuel pump unit. Still I'm experiencing the same delayed start issue. When they plug their computer terminal to the vehicle OBD2 port, error is reported as "Vehicle Starting Issue".

Note: I cleaned my injectors manually, Cleaned throttle body, there are no vibrations, engine is running at optimum efficiency.

I really appreciate if somebody can at least give me a clue for the delayed starting issue.

Cheers..