ok guys so my friends car has a problem with surging

it will idle fine for a few minutes, but then it will surge up and down after a while

valves, were recently replace and timing belt, tensioner and tensioner bolt. i have no idea what would make it do this at least not the idle fine for a while then do it

 

is ur engine light on? if so read the code and go from there. if not check for a intake manifold leak or vacuum leak

 

he put on a hondata IM gasket could that be causing a leak and causing this? maybe a faulty gasket?