KA24DE Issues

[Tuvara]

Ok, the question may be as old as time itself, but my meger search abilities on this forum haven't turned up a sufficent answer to the issues at hand.
My brother recently aquired a '93 240SX Convertible, everything was fine for a few months until the fuel injector that was suspected to be bad got replaced, after the new injector was put in the car ran well until this last month. The car now runs fine if it has sat for a while or hasn't fully warmed up, when it gets to full operating temp, it begins to lag, shutter on idle, stall and die, and surge repeatedly followed by stalling out. Now the strange part is that if the car is cutt-off and then restarted the car runs fine again until the problems inevitably return. One of the first symptoms was that the car seemed as if it did not want to shift from 1st to 2nd.
We reset the ecu yesterday using a write up I had found in a thread with one of the symptoms, but not all of them, the ecu gave the all clear after the reset, and the car ran well for an extended period of time, but as every time before the problems returned.
If anyone reading this can suggest a solution or has had similar problems that were resolved by a mechanic I'd appreciate the suggestions, this car has only 70,000 on the odometer and my brother would love to keep the car, the problem is that the car is his only means of transport and has to run correctly, other wise he'll have to get something else.

[biggie]

Replaced the ECU temp sensor?