I have a 1997 explorer with a 5.0 and awd. It has a very rough idle and jerks when the rpms is below 2,000. At idle it surges from 4 or 500 rpms to 8 or 900 rpms. I have replaced the iac motor, egr, egr back pressure sensor, cam sync., cam position sensor, egr regulator. I have new plugs, wires...