Because　of　the　increased　residual　gas　fraction　and　low　combustion　temperature,　the　traditional　spark-ignited　(SI)　gasoline　engines　tend　to　encounter　the　dropped　thermal　efficiency　and　increased　emissions　at　idle.　This　paper　experimentally　investigated　the　effects　of　hydrogen　addition,　cylinder　cutoff,　lean　combustion　and　idle　speed　reduction　on　improving　the　combustion　and　emissions　performance　of　gasoline　engine　at　idle.　The　tests　were　conducted　on　a　modified　1.6　L　SI　engine　equipped　with　a　hydrogen　port-injection　system　and　a　self-developed　hybrid　electronic　control　unit　(HECU).　In　the　experiments,　cylinder　cutoff　was　realized　by　stopping　the　hydrogen　and　gasoline　injections　to　the　specified　cylinders.　The　HECU　was　adopted　to　control　the　opening　of　idle　bypass　valve　and　spark　timing　at　the　reduced　idle　speed　of　600　rpm.　The　test　results　showed　that　hydrogen　addition,　lean　burn,　cylinder　cutoff　and　idle　speed　reduction　were　all　effective　on　decreasing　the　engine　fuel　consumption　at　idle.　Under　the　given　test　conditions,　the　combination　of　cylinder　cutoff　and　hydrogen　addition　was　the　most　effective,　which　reduced　the　fuel　consumption　by　33.25%　at　a　hydrogen　volume　fraction　in　the　intake　of　2.87%　and　two-cylinder　cutoff　mode,　compared　with　that　of　the　original　engine.　Moreover,　engine　cyclic　variation,　HC　and　CO　emissions　were　also　decreased　after　hydrogen　addition　and　cylinder　cutoff.　Because　of　the　dropped　combustion　temperature,　NO　emissions　were　decreased　at　the　lean　combustion　and　decreased　idle　speed.　However,　due　to　the　increased　residual　gas　fraction　and　weakened　charge　flow,　HC　emissions　from　the　engine　operating　at　an　idle　speed　of　600　rpm　and　a　hydrogen　addition　fraction　of　3.20%　were　slightly　higher　than　those　from　the　original　gasoline　engine　at　idle.　Copyright　(C)　2011,　Hydrogen　Energy　Publications,　LLC.　Published　by　Elsevier　Ltd.　All　rights　reserved.