Vitz/Yaris 2006 1.0 version Stalls at low rpm

[asimaleem]

For the last two weeks , my vitz 2006 model (1.0L 3-cylinder engine 80K Kms done) stalls quite frequently (but not always) at low speed/rpm especially when foot is taken off the accelerator paddle usually before or after the speed breakers , traffic signals ,turns etc i.e. at low speed and rpm. Once stalled , car starts after a very long cranking on 1st or 2nd try. There is no "check engine” light or any other indication showing up. This problem has started to happen immediately after I did two things:
1). Fuel system treatment used (Liquimoly)
2). Fuel filter changed by Toyota 3s ,2 days after Fuel system treatment

According to my driver, the frequency of stalling increases whenever fuel tank is refilled (could be a coincidence). Also according to him car is creating more air pressure than usual in the fuel tank.(again he could be wrong).

I have shown this problem to Toyota 3S but they have not been able to diagnose it correctly yet and following has been done so far:
• Throttle body serviced
• Computer scan done - No problem found during computer diagnosis
• Fuel pump checked -generating normal 300 pressure

But the problem still persists! . Any idea what is wrong?