engine misses

[240sx2488]

i build an ka24e and everything on it is brand new except for the iia unit and air regulator and i can crank it up it drive it and it want miss it will run great and when it gets to normal running temp it starts missing you can push the pedal to the floor and it will do nothing but miss and then you can change the ecu and it will run great for 2 mins and do it again

[Bwana]

Have you checked for vacuum leaks? Also ensure that your fuel pressure and timing are correct. A vacuum leak or MAF problem would be my first guesses though.