I find the EECIV system very diffcult to diagnose. And the very first systems they came out with can be very primitive, some with no fuel test port on the fuel rail, none of them had working check engine lights, and my 86 ranger relies on switches on the clutch pedal and the shifter to determine idle strategy for the computer. When these switches go bad or are not connected during a swap, that's when you get the little weird things going on during idle and tip in on the throttle. Later on they changed the programming I believe, and used the speed sensor more for determining idle strategy.