2001 Hyundai Elantra Engine raises

Engine Performance problem
2001 Hyundai Elantra 4 cyl Automatic 93000 miles

My 2001 Hyundai Elantra GT has the check engine light on. It had happened previously too, but there were not other issues. The light would go off after some time.
But this time, after two days of check engine light, the car just raises automatically without me stepping on the gas. It raises and calms down in regular intervals (maybe a second high then low, again high and then low.). I somehow drove it home and had a tough time driving it. But it would drive smooth once it gains speed and changes gears (returns to normal RPM). Having problems at STOP signals, I have to literally stand on the brake pedal! Any suggestions?