Yeah I have something similar on my GTR. It runs well on boost but down low, and when its cold especially, it runs like a rex. sputtering etc. I had a 180SX about 8 years ago and the same thing happened on that. It ended up being the coil packs which continually failed (I replaced them about 5 times in 2 years!). It got so bad that the car would randomly run on 3 cylinders!
I have heard that if the engine has been steam cleaned then it can kill the coils (even with the coil pack cover on). A replacement coil (assuming there is only one dead) would be cheaper than an ignition modual though I guess.
Heat also affects them.