I took my 94 Jimmy 4.3l cpi to 2 different shops, it surges or lopes and stalls at idle, it also stalled on the road about 45 mph and would not start (had to have it towed). Now it starts but runs bad sounds like it's missing. One mech. changed the iac (no help) he said it might be the eng. harness or the ecm but he is not sure. The other mech. (diff. shop) said it has a rod knock and there is a knock sensor that retards the timing and this might be the trouble. He said the rod knock means I need a new eng. Anyone have any ideas, how do I check the ECM and the harness, anyone know someone in Bergen county N.J. that might be able to help.Sorry for the long post. Thanks BILL