oil light is flashing after overhauling engine

Hi! i own a JDM suzuki alto with a Turbo F6A SOHC engine recently overhauled. since last 10 days i have noticed the engine oil light on the dash lights up when the car is idling after the engine has warmed up. however when above idle RPM, the light does not come on. The problem developed after engine overhaul with new pistons & rings. the engine has an EFI management system and is turbocharged.