Put in rebuilt engine 2 items...

[fixkick]

So strange.  My CEL does come on and turn off after start.  

The RPM is not effected by turning on the heater and it doesn't do the same thing in Reverse making that even stranger.  

I think the second cable must be unused but could be used by a cruise control or something.

the car with 3 speed has 2 cables,  1 is throttle and other is the 3speed kick down cable.   the 3rd cable is always the optional cruise control .
I can see after 24 years the cruise motor drive burned out and last guy parked it to curb. sure. and sure left part of cable there?

bad tacho I'd say.
or bad wiring to it.
the tach has 3 wires,  ground, 12vdc power and the brown tacho input wire called spark primary pulses, from the spark coin and the noise supressor.
many of these tachs, now are dead or 1/2 dead,  it can not bad bad brown wire signals or the engine dies. and if tacho brown wire goes dead he ECU sees that and cuts fuel to avoid a fire.
all cars do that, modern EFI,  no spark cut fuel in 1/100th of second flat. (to prevent as seen on TV crash and burn.,  )

the engine is ok, the sparks ok the car drives ok and idles ok at 800 hot, but the tach lies. so the tacho  is no good. (or the wires to it, can fail (rust happens)
why the shifter affects this no clue by me.  (actual rpm is ok at all times)  if the engine actually slows down below 800 hot (750 ,min) then that is a problem,

if other gauges all read right the tacho has full power, both wires, 12v and ground. so the caps in the tacho dried out just like he ECU love to do.