I have low power on take off

My 1999 Ford Festiva is regularly serviced, however it has started to have problems with no power to take off after slowing down and idling in traffic, it also appears to cough. It is an automatic and I almost have to push the accelerator to the floor to get going. When slowing down and idling in traffic it has almost no takeoff power I have to creep along or plant my foot on the accelerator to get going, it also appears to shudder when idling. I recently almost ran out of petrol and wondered if some muck from the fuel tank could have dredged into the motor, if so what to do? Or could it be something more sinister. It's an automatic. Thank you Robyn