Engine Performance problem
2002 Other Ford Models 4 cyl Front Wheel Drive Manual 75,000 miles

had car 1 week. it started surging and not running right after a short drive. took back to car lot. put on diagnostics machine. replaced with a "used'"coil pack. still won't run right with heater/a/c on. service engine came on with surging problem. thought it would go out with replaced coil pack. now what?? it is a 2002 ford escort zx2