Arthur and Paul,
I peeled back the insulation on the engine wiring harness on the firewall above the engine and the wires all looked fine. They were flexible, no insulation showing so I'm guessing that it's been replaced at some point.
BUT........I just rechecked the codes and it came up with a code 40 out of socket 8. According to my PM disc this indicates a problem with the Trans. overload switch. Do you think the stumbling idle may be related to this code?