Leaderboard

Modern EFI systems do not generally have adjustable idle settings in the classic sense--I.e. some mechanical adjustment as with carbureted engines--instead the idle speed is controlled by the electronic engine management system. Most often this a accomplished via an idle air control (IAC , Hisun seems to call it an "idle speed stepper motor") valve operated by a stepper motor or duty-factor controlled spring-loaded solenoid valve that controls the amount of intake air allowed to bypass the throttle body main damper ("butterfly"). IAC valves are usually mounted on the throttle body. The idle speed setting is accomplished by reprogramming the engine management system--not by turning a screw or manipulating some other mechanical device IAC mounted on the throttle body (this is from the service manual for my HS400): Hisun EMS schematic: Components: Idle too high = too much air passing through the IAC valve or leaking into the intake tract between the throttle body and the intake port on the cylinder head.. This can happen if the IAC valve sticks or otherwise cannot operate freely--or-- if air is leaking into the intake manifold "after" the throttle body. Check that he intake gaskets, tubes, etc. are tight; If you feel competent to do so remove the throttle body and make sure the IAC operates freely.