Abstract This work aims to improve the idle performance of the n-butanol rotary engine by blending hydrogen and reducing idle speed. Hydrogen volume percentage (βH2) changes from 0 to 7.94% and the idle speed decreases from 2600 to 2400 rpm. The test results show that the engine can achieve better stability and economy due to the coupling effect of mixing hydrogen and reducing the idling. The total fuel flow rate reduces from 24.57 MJ/h at 2600 rpm when pure n-butanol is fueled to 19.35 MJ/h at 2400 rpm when βH2 equals to 7.94%. The period of flame development and propagation are observably decreased by blending hydrogen even if reducing idle speed has a few negative effects. Hydrogen enrichment is an effective way to reduce the emissions of CO and HC. Besides, the negative effects of reducing idle speed on HC and CO emissions are decreased to a negligible level when βH2 passes about 7%. Besides, NOx emission is maintained at an extremely low value in the testing range. Also, enrichment hydrogen can compensate for the negative effects on combustion and emissions of reducing idle speed.