I have a 2005 MPV with 170K miles on it. I while back I noticed it was stumbling under load. I found the intake boot (past the mass air filter) was cracked, so I replaced it, and put in some STP fuel additive. That made it a lot better, but it's still stumbling a bit. On this last 4 hour trip, it only started stumbling after about 2 hours on the road, and then only pretty rarely. If I'm holding steady RPMs it goes fine, but if I let off the gas for a bit, then try to accelerate, it will sometimes stumble slightly a couple of times.
I drive like a grandma, so I'm not slamming on the gas, just lightly accelerating. Any ideas? Another vacuum leak somewhere?

 

Sounds like a bad coil. Do you know when they were last replaced? It’s a pain in the butt as the intake manifold has to be removed to get to all six. But I’d look there first.

You may notice a worsened MPG which would be an indicator. They can be really intermittent, with the problem seeming to go away for a month, only to return. Should be able to get the job done for around $500 if you shop around. Or follow a YouTube tutorial. I’d recommend the Denso top end coil packs and the best spark plugs you’re comfortable with (opinions vary, I use NGK) to avoid having to do it in the future.

while it’s “not the done thing” you could also just replace the four you can reach and hope it’s one of those. You have a 66.6% chance of winning.