i've just installed a vafc on my car while i'm waiting for my engine to be properly break-in before putting back the turbo and i notice my rpm reading on the vafc wasn't steady at all. it goes up and down +/- 10rpm and sometimes more during idling BUT my tach needle is steady at all. so is this behavior normal? is it because it's digital? the engine is completely stock right now with just an HKS air filter.

 

mine does the same thing. i'd say it's normal.

 

mine does the same...pretty sure it's normal.

 

Its perfectly normal. You Tach needle is steady cos its analogue and the +-10rpm is too small a change for the Tach needle to be affected so its steady. Where as the AFC is digital and very accurate, work by the 'unit', so it will detect every 1rpm change in the rev range, hence the constant rpm variation you see on the AFC readout

 

ok thanks guys. good to hear it's normal.