I too am having an issue with same symptoms. I also have issues with the heat and a/c in my car when my 88 corvette 4+3 35th anniversary edition 5speed is in neutral or gear it’s thrown off if the heat and or a/c or even defrost is on and I’m new to driving stick, and new to owning a corvette too, plus have little experience with engines or how they operate in general. I’m hoping maybe you have found a resolution to the issue? Or if not, do you also have the issue with heater and ac? Maybe they are linked to the same thing needing fixed?