Howdy,

First, let me tell you that I have limited experience with the Bosch FI systems. But, I've been reading schematics for more years than I care to admit and I've been dealing with FI systems for almost as many years on various cars.

I want to make sure I am on the correct prints for the system; LH2.0, correct? If so, the extra blue wire in the harness is probably meant for an EGR, not used in '84. That is really the only explanation I can come up with for the blues.

For your current problem, rough idle, you don't mention two items in your list of things replaced or checked. One is the idle position switch. Did you check that for ON/OFF with throttle position? The other is the purge canister. It has a vacuum diaphragm that, if leaking, would introduce unmetered air.

The check back to PIN2 of the ECU: I have looked at every schematic I have for why you would be checking the GN-W wire to the ECU at PIN2. I cannot find that connection anywhere. PIN2 is shown as a BL wire coming back from the temperature sensor. (PIN2 on the Lambda-sond Control unit is shown as a solid GN wire.)

Do you actually have a GN-W wire on PIN2 of the ECU? If so, I can find no reference for that connection. Every schematic I have shows PIN13 as the current source for the injectors.

Regardless of the pin on the ECU, to check the injector drive circuit wiring you should isolate all four injectors. Else, you will have sneak paths all over the place.

I would not ordinarily suspect the injector drive circuit for a rough idle. The number one reason for rough idle is unmetered air. Second would be incorrect information from a sensor. Either problem can be caused by bad wiring, of course. But each sensor and actuator should be verified stand-alone. I would not replace the harness just because I have one on hand. You do have evidence of brittle insulation and broken conductors and that certainly justifies replacing the harness. But, I don't think it will address your current symptoms.
--
Mr. Shannon DeWolfe -- (I've taken to using Mr. because my name tends to mislead folks on the WWW. I am a 51 year old fat man ;-) -- KD5QBL