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 (λ) 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 λ.