Intermittent engine surge/hesitate while on traffic light

SOURCE: Ford Focus ZX5 - Rear brake lights stay on when car is running and in gear

Hi, you have suffered a major electrical short here, and the car is telling you via the light signals that you need to take care of this in a garage. The original short burnt cables, which is why there is visible signs of melting, smell etc. I know it will involve a cost, but consider the value of your life if the car was to go on fire with you or your family in it? Another short will cause such a fire, get to a garage soon!

SOURCE: ford focus keeps stalling

I suspect it is a problem with the evaporative emission system. Basically, it collects vapors from the fuel tank and stores them in a charcoal canister in the engine compartment. It thens purges them into the engine when the engine is warm and running at road speed. You may be dumping too much vapor because your canister is filling with fule as well as vapor.

Do you try to "nurse" teh tank full at the fuel station? If yes, you may be flooding the canister.
Try just filling it 3/4 each time & see if problem goes away.

SOURCE: How do I change fuel filter.

run a fuel pressure test, and check the fuel pump relay, in the underhood power distribution box, if relay is good and you have power at the pump with no fuel pressure then you have a bad pump

SOURCE: MY 2005 FORD FOCUS ENGINE LIGHT IS ON .... WHEN I

you should have the code read with a scanner at a garage Possible (Throttle position sensor ??? (TPS) the code reader will tell you exactly wich sensor is the problem

SOURCE: 01 Focus 2.0 split port engine. Service engine light on!

uplug air metering sensor car should run almost normal but will set check eng, light