revs limited to 2,800 rpm in 1993 MX-3 (4 cyl)

[Civic driven01]

I dont know if anyone here can help, but a friend of mine has an old 1993 MX3 with the 1.6L 5spd. It runs fine except it stumbles when the rpms reach around 2,800 rpms regardless of what gear its in or even if its neautral. Its like theres a rev limiter there but not really. Its like its losing fuel or ignition at that partucluar point in the rpm range. Brandnew cap rotor, plug wires, ecu, map sensor, and distributor have been replaced already. I believe the distributor was replaced with a used one though. no sign of any check engine light. As soon as it stumbles at 2,800 the engine quick regains and remains running. This problem occurred out of the blue since it has occurred it has been 100% consistent. It seems like an ignition problem of some kind to me, but I'm not a certified mechanic who works on mazdas everyday. Its a beater but its his only mode of transportation and hes a good guy, that I'm trying to help out. thanks in advance.

[Fud]

Check your cat (if it's blocked) and distributor!