Toyota Corolla 2001 auto vibrates/hesitates on start as if lacking gas

My Toyota 2001, hesitates each time i start engine as if it will stall. Need to crank two or three times to be able to start engine.
Need to pump on gas pedal to start engine , lacks power and hesitates.
I am suspecting a clogged injector as can hear sort of misfire /knock when accelerating to make car move forward.

Problem history
Installed a multipoint lpg kit 2 years ago. Got a start problem some months ago as was low on gas. That's why suspecting a clogged injector coz when car switch to lpg automatically after start I don't get the problem. Its only when i start the car after switching it off that it hesitates.