Hi i have a 1986 Nissan pickup with a z-24 T.B.I motor, i cannot figure out why the idle surges about 500 rpms. it will surge from around 1200 rpm to 1700 rpm it just rises than falls over and over doesn't miss or hesitate and does not have a dead hole. no check engine light or over heating, almost seems something to do with the electronics with T.B.I?? can anyone help me with this one on figuring it out?