[Rick Lee]

Are you still not getting a CEL with those codes? In my 993, when I had readiness monitor issues, part of the cat warm-up check was to start the car cold and let idle for (IIRC) two minutes before moving. The communication failure is probably a transmisison to engine wiring issue, if it's a '99 Miata. Do those have CVT trannies? I don't think so. If CVT, then you might need either a software reflash or a reprogram by doing a ridiculous drive procedure like I had to do with my 993. Our old Mini dealer did this for my wife's car, even though it wasn't a factory-authorized procedure. They came up with is on their own and it worked like a charm.