i just replaced the idle air control valve on a 1990 mustang gt. after replacing it, there is still a surge in rpm's when i am driving on the street or freeway.it only does this once in a while. on the freeway, when it surges, the car kind of jerks until the surge goes down. please help! this is the only car i have. let me know a.s.a.p. . hector5.0