Lower costs at the petrol pumps were offset by an upward contribution to the Consumer Prices Index (CPI) from air fares, including an increase for domestic flights.
The figures from the Office for National Statistics (ONS) will be disappointing for policymakers hoping to see inflation start to fall towards the Bank of England's 2% target.
A separate measure of inflation, the Retail Prices Index, fell from 3.3% in August to 3.2% in September.
Petrol prices fell 0.2% over the month, or 0.5p per litre, to stand at £1.37 a litre. This compared with a 2.7% rise for the same period in 2012.
However, the decline in air fares, usual at this time of the year, was smaller than normal for long-haul and European flights, while domestic flight prices rose.
Elsewhere, education inflation reached an all-time high of 21.4% since records began in January 1997 as new rates for evening classes and private schools added to the ongoing impact of tuition fees.
Food inflation stood at around 4.8%, still well ahead of wage increases but little changed on last month. Fruit and vegetable price rises nudged up, driven by plums and organic apples, as well as cauliflowers, onions and premium potato crisps.
Other foods including bread and cereals, fish, jam and chocolate had a downward effect.
A recently introduced experimental inflation measure, CPIH, which includes housing costs, was static at 2.5%. Another experimental measure, RPIJ, fell to 2.5% from 2.6% in August.
The recent announcement of a tariff hike by gas and electricity supplier SSE - the first such move by one of the Big Six energy firms this year - has raised fears of upward pressure on inflation.