Camry :: Engine Jerk In / Out Around 40 MPH When Touching The Gas

For a few weeks now, the '02 Camry has had the engine jerk in/out around 40 MPH and 60 MPH when touching the gas just enough to hold speed (only when engine is warm & car has gone to closed-loop mode). If you mash down more on the gas, or accelerate through these speeds with more pedal pressure, it will pull perfectly smoothly away from those speeds, and the engine runs smooth when it isn't doing this.

Plugs have never been changed, but I will wait and do that when it is warmer outside. They are not the problem.

The other night, it seems to have gone into limp mode - will not drive over 10 MPH or rev above 2200 RPM in park, throwing a code for a throttle position sensor (P0120). I replaced the throttle position sensor with Duralast part (that didn't fit), then another genuine Toyota sensor. Still no luck...even clearing the code, it immediately returns upon starting the engine.

Throttle body and mass airflow sensor were both cleaned - actually, neither were gunked up badly. The car won't even start or run without the MAF plugged in, and there was no MAF code. I can't find any broken vacuum lines or obvious air intake leaks (the one thing I haven't checked is the intake manifold gasket).