Reviving this thread as I am having the before mentioned problems with my FJ40, but none of the issues discussed above seem to be helping. Had very similar issues with the Sniper leaning out to ~35% and backfiring previously, but a new O2 sensor fixed the problem. This time around the issue started suddenly one morning on my wife's commute to work and a new O2 sensor has done nothing to rectify the problem. Truck starts and idles great, but when put under load she leans out to ~35%, coughs up a good backfire, then slowly sorts herself out. Happens at low RPM (~1000,1500) pulling away from every stop sign. When cruising, if I go above ~40% TPS she sounds like she's misfiring and looses power until I reduce throttle. I've had similar issues on my FJ60 and never really figured it out, but the 60 isn't this bad. Sprayed an entire can of ether around everything sniper related and I get no RPM change, so I'm confident I don't have any intake or exhaust leaks (this is also true on the 60). When looking down the throttle body at idle both BBL appear to have a nice and consistent spray of fuel floating around the butterfly's so I'm not thinking one injector is failing. Just for kicks I swapped out the Corvette filter/regulator with my spare also with no change.
I ran a log of her miss-behavior on my drive home from a buddies today after failing to stumble upon any fixes, should anyone be willing to download and open a file from a stranger (I would look myself, but I have a Mac so I can't download the app).
Thanks!
Clark