Chasing 87' TBI idle problem. Included service code

[chevymotocross]

SS Delux, you are correct, I was reading the flashes wrong. It's not a code 13, it is a code 33 which would indicate MAP sensor issues.

I inserted the paper clip in terminals A and B. Turned ignition on. It flashed once, pause, 2 flashes which indicated the code 12 diagnostic mode. It did this 3 times. Then, it flashed 3 times quickly, pause, and then 3 times quickly again. It repeated this a few times and this was the only code found.

Thing is, I think it only stored this code because when it's about to die, running like poo, it is making low vacuum which triggers the light. It stalls, restart the engine and light is off because it idles fine again. I can see the MAP sensor being bad if it always idled poorly like that, but it only happens with the A/C on, in gear, not moving.

Is there any way to test a MAP sensor w/o simply replacing it? Seems from a few of your experiences, the ECM doesn't accurately point you to the actual cause of running like poo.