The　idle　lean　burn　characteristics　of　a　port　fuel　injection　(PFI)　spark　ignition　(SI)　engine　fueled　with　gasoline　and　methanol　was　experimentally　investigated.　An　idle　lean　burn　control　algorithm　was　developed　to　keep　the　engine　speed　around　800　rpm　and　maintain　the　excess　air　coefficient　(lambda)　at　1.0,　1.2,　and　1.4,　respectively.　The　spark　timing　was　adopted　according　to　the　maximum　indicated　thermal　efficiency.　The　results　showed　that　the　SI　engine　fueled　with　methanol　illustrated　better　lean　burn　performance　than　the　engine　fueled　with　gasoline.　Compared　with　the　engine　fueled　with　gasoline,　the　indicated　thermal　efficiency　(ITE)　of　engine　fueled　with　methanol　was　increased;　the　flame　development　and　propagation　periods　were　shortened;　the　coefficient　of　variation　in　indicated　mean　effective　pressure　(COVimep)　was　decreased,　and　the　emissions　of　HC,　CO　and　NOx　were　decreased　at　each　lambda.　(C)　2015　Elsevier　Ltd.　All　rights　reserved.