The goal is to figure out what the engine needs, not necessarily how the components on the engine are doing. Once the engine's needs are understood then you can chase down components related to that issue. Eliminate the computer's ability to respond in order to control what the engine gets. Then you can set the engine's timing, and you can increase or decrease the fuel delivered to the engine. If the engine only runs well with twice as much fuel as the ecm is delivering then you can work on solving that problem. If the engine only runs well with extra spark advance then you can work on solving that problem. It's too easy to lose sight of the goal when approaching the problem at component level only.
If you are able to get steady rpm by disconnecting the tan/black wire then you have the ability to see if the engine runs reasonably well or if it still has a problem. Once the timing is set you can look at fuel to see if more or less will improve the situation. If you find a method to add or subtract fuel, and the engine runs better, restore the ecm's ability to adjust timing and see if the problem returns with your fuel adjustment still in place.
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