My ford fucus either wants to choke off or rev up. can anyone help?

Question

it doesnt do it all the time so the local repair shop is having a hard time pinpoiting problem. sometimes it chokes off at redlights and sometimes it revs way up. if anybody has any idea what this could be, please help.

Answer 1

the soft rubber hose from the intake to to the pcv valve is damaged it is on the back side of the engine  

Answer 2

fuel filter  fuel system flush .. bad gas

Answer 3

check mass air flow connector

wire may break when u change air filter