Vague symptoms, how to handle?

[SiennaDriver]

The Sienna sometimes suddenly starts running rough when stopped, like at a light. It almost seems like it's about to stall, but stepping on the brake and lightly on the gas at the same time brings it back to normal, or if not putting the car in N and stepping on the gas will bring it back to normal.

Sometimes on acceleration the van will also run rough, but once it reaches speed it's fine.

Is something on the way out?

[Cranky-Condor]

And it's not throwing any codes? Anytime our 2000 even started to run bad the check engine light comes on.