help with my tach

my tach's needle keeps bouncing no matter if i have my foot on the gas or on the brake please help me out guys is this an electrical problem if so can you guys tell me how can i fix it

does the needle just bounce. or does the engine rev up too ?

if the enginge is revving .... I had this happen with a friends car - the idiots at Honda )service) replaced his EGR and forgot to bolt it on, so it came loose a few days later.

the needle just bounces no matter if the engine is reving or not