iceshake

Hi Guys, thank you for letting me post in this thread. I just owned a 1997 subaru forester (japan) stb, converted from RHD to LHD. And just recently, i am experiencing this problem: when I crank the engne it will start up easily and smoothly, but as i step into the pedal to move, the car will jerk to an almost full stop, but if i press the gas, it will still go and will never jerk again all throughout the trip. but when i pulled over at a gas station which requires to turn off the engine, it happened again as i leave the station, and keeps on happening when i turn off the engine and turn it on again, regardless it its cold or in normal temp already. what should i check to know and solve this problem? Thank you in advance guys, Im from the Philippines btw.