The headline purchasing managers index rose from 55.7 in August to 56.2 with numbers above 50 indicating growth.
The new orders index fell from 63.2 in July to 60.5 in August. Production expanded two ticks faster with the output index for September at 62.6 after a reading of 62.4 in August.
Employment showed faster growth with the index measuring the number of employees climbing from 53.3 to 55.4.
The institute said 11 of 18 manufacturing sub-sectors indicated they were growing in September.