2500rpm is the magic MAFS number. This is the engine rpm limit when it can't find the MAFS. It runs really rich so that you don't blow it up, which is what is causing all the black smoke.

Now to the ECU. You can start off by listing the motor type (redtop, etc), the large number on the ECU cover, and who did your harness. The fact that it runs means that you atleast have an SR ecu (or atleast, not a KA ecu). You can go one step further by putting the ecu in diagnostic mode. To do this, flip the ecu around and find the hole that you can stick a screwdriver in to. This is the potentiometer. It'll either accept a large slotted screwdriver or a very small phillips. Turn the car to ON (not started), turn the potentiometer completely clockwise, pause 2 seconds, and then turn it back to counterclockwise. It will start flashing a code to you in long and short blinks. The code is 2 digits. Long blinks make up the first digit, short blinks make up the second digit. There may be multiple codes, so write them all down. Once it starts to repeat (or stops), that's all of them. Turn the potentiometer clockwise and back to return to normal mode.

So, post all the ECU info and codes, and we'll point you in the right direction.