Surging only in neutral with a manual? On a 91? Is the neutral safety switch (It should be in the transmission. NOT the clutch switch. They share a wire color.) hooked up and working?
That is a good question. In fact, awhile back when I did the EEC-IV test, I did see a code pop up for the neutral safety switch.
Take a look at these photos. I only see one switch that is "plugged in" - air quotes because it looks to be partially smashed and just barely connected. Is that the neutral safety switch? Or maybe the reverse light switch, or something else? It is on the driver's side. The pins are cylindrical (Pic 2) and the two wires are purple with an orange stripe and black with a pink stripe.
Strangely, there is a connector that branches off of the wiring for the first switch that I mentioned that is just hanging there unplugged (see Pic 1). Any idea what that is the connector to? On the passenger's side of the transmission there is what may be another mangled plug of some type. It almost just looks like a bolt, but the inside appears to be broken plastic (see other pic). Maybe this is what the other connector is supposed to connect to?