99 Ford Escort ZX2 surging problem

My wife was on her way to work this morning when the Service Engine Soon light came on. She continued on her way and the car started surging when she was going 50-55 mph. Also the service engine light began flashing. On her way home the car continued to do the surging thing but worse. Now I took it for a spin and the car seems normal although the service engine light is on. Is it possible I got some bad gas (maybe with water in it) as I filled it up last night? Or is it possible the gas cap needs to be replaced as it doesn't click when tightening. I put some gas line antifreeze and fuel injector cleaner in the gas tank also

Thanks in advance

The source of the check engine light and the surging could be different. Most cars I believe will throw a "Excessive evaporation" error and turn on the check engine light if the gas cap isn't sealing all the way or isn't closed all the way.

you can clear the error by disconnecting the battery for 15min.....if the light comes back then you know there is still a problem with the car.