Whenever l stop at a light or stop sign my focus jerks and feels like its gonna stall.None of my lights are on and l took it to a mechanic and ofcourse it didnt do it when he drove it around.He couldnt tell me whats wrong,he kept asking me about idling,l dont have an rpm meter in my dash and l dont know what idling is?Any help?
it does do it in park,and it actually stalled out today while in park.Ive never tryed it in neutral.

good questions

idling is basically when your car is on but not in gear and not moving. (basically P or N for auto and neutral for stick).

If you find that the car idle is rough (makes strange noise, idles laud and stuff like it it might be a belt or oil problem)

From your description l am thinking there is something wrong with transmission. Sounds like your clutch is slipping. IF you have auto then to get this fixed is alot of money. Stick not so much.

it could also be in the fuel that when your not on the gas it might be starving the engine or you might need to change your air filter or it could be in your transmission does it do it when your in park or neutral

No help. You do not give us enough info.

Anyway, you need to leave the car with a tech long enough to let tehm drive and have symptoms show up.

Or you can make use of this wonderful intraweb and google search a Ford Focus forum, register, and post your story there.

l would have the guy look at the rubber pcv line that runs from under the intake to the pcv itself the elbow of this tube that connects under the intake usually tends to collapse and get very soft and gets a hole in it causing a vacuum leak it will not always trigger an engine light. If that is ok have him do a power balance test these care also tend to have bad coils, or wires or a bad spark plug, but l am guessing that the pcv tube is leaking

Chances r u have a vac leak. However try this 1st.Fill ur gas tank with a mid grade octane gas..not reg like u have been useing..add a good bottle of fuel injector cleaner (Gumout makes a good product). You will see a big diff in the preformance of ur engine in app 25-50 miles of driving.While doing this to clean out the fuel injectors,if it still feels like stalling at stops..simply put the car in nutreal. Now if after burning a tank of gas & the problem is still there,then u have a Vac leak & it needs to be tracked down & corrected. l have a 2000 Focus ZX3 & it did the same thing.It cost me $38 at a Ford dealer to fix.