According to widipedia:
During step 1 (isothermal heat addition or absorption) the gas is allowed to expand and it does work on the surroundings. The temperature of the gas does not change during the process, and thus the expansion is isothermal. The gas expansion is propelled by absorption of heat energy Q1.
The gas temperature is the same as the temperature of the reservoir. But where may heat energy Q1 come from as there is no temperature gradient between gas and reservoir?