4A-GE MK1 Engine Engine sputters @ 3000 RPM, help!

4A-GE MK1 Engine, engine, cleaned, sensor, sputters, 1991, years, 3000, corolla, swap, japanese, months, 3000km, started, ideas, cost, injectors, fuel, time, few&8221, &8220a, deal, changing, thinking, stored, catch, smooth, won&8217t, runs, pretty, 1986, accelerating, rich, black, decently, idles, flow, mass, plugs, exhaust, smoke, i&8217ve, replaced, spark, filter, replace

My 1986 MR2 engine sputters when accelerating and gets especially bad around 3000 rpm, and pretty much won’t run smooth after that. It also runs very rich and some black smoke from the exhaust. I’ve replaced the O2 sensor and air filter, cleaned the spark plugs and mass air flow sensor. Car idles decently well since I cleaned it up. The catch is that 10 years ago I replace the engine with a 1991 Japanese Corolla GTS engine. the swap went well for about 3-4 months, say 3000km, the it started