2003 ssei with 171k, always run premium. I'm at about half tank and I just noticed this issue on this tank of gas. I'm in MN and temp is just below freezing. Car runs fine under moderate to heavy accel, but at about 75% throttle you can give it more gas, the car won't respond, and it actually loses acceleration and what feels like a miss, or an audible difference in the way engine is running. Perhaps the engine is trying to advance the timing to the point where it just starts to detonate? No CEL, no misfires. Plugs and wires have about 80k on them. I'm planning on running through this tank of gas, and try it again. If it still is happening, perhaps I'll replace plugs and wires. I ran a bottle of amsoil fuel treatment at the first of the month as a preventative measure. Fuel trims are fine. I thought I'd run it by the experts to see if they agree with bad gas. Car has an aftermarket MAP, TPS, and MAF, and ignition module, but the engine is stock except for a drop in K&N.

Ya when I hear on this tank of gas then issues, it is good to assume something'* up with the last fuel up.
Many premium fuels still contain ethanol, which likes to absorbs moisture. Who knows what was in the last tankful as well.
So, I would try a water remover product like Heet, with injector cleaner, & see if that helps.

I am glad that you do not have a CEL.
I would tho recommend replacing the spark plugs. By 80k miles, gaps will no longer be in spec.
New plug wires, not a bad idea as well.

Maybe a coil issue? Corrosion sometimes occur at the electric connection of the coils. It is fairly easy to inspect, just takes a few moments. Surprised you are not getting a misfire. flashing check engine light when the power fades.

So nice thick air, lots of oxygen.

So maybe gas isn't so bad?

. . . now the throttle plate is more open and vacuum is going down. More air going in more easily, and lower vacuum should have the fuel pressure regulator add more fuel.

Makes me want to ask: How'* your fuel pressure regulator?

. . . and I agree, if these plugs have more than 80,000 on them or you are unaware of their status they should be replaced . . . and may as well replace wires while you're at it.

And yes, maybe the fuel is less good than previous, and maybe in combination with a marginal fuel pressure regulator this issue is popping up? I just can't get over the part where it runs fine at idle (I assume) and at moderate/heavy acceleration below 75% .

. . . and the fuel pressure regulator is easy to replace, and it probably needs one anyways if you are unaware of its status.

I didn’t get any heet before refilling at a different station. I tried it a couple times on the way home. The first time no issues, but a few miles down the road it was back, so might say intermittent. I hadn’t considered the FP. I will do a regulator too. Thanks for the suggestions. I’ll update again once I get the plugs wires and regulator swapped. I had tested coils awhile back but there could be a weak one by now. I have a few spares of those. I think there is a station that has true no ethanol premium I should try too.

Update: Put in a new set AC DP plugs (no iridiums on hand) New Belden wire set, bottle of heet
Drove it around the section and the problem was still the same / unchanged. Drove to get gas and with the torque converter locked under light acceleration, there is a hesitation / jerk now feels like tc trying to unlock but doesn't. MY CEL is on due to a downstream O2, but I don't think that is the cause of issue. Filled it with no ethanol premium and on the way home and now it is missing bad under acceleration with a flashing CEL and P0300 multiple random misfire. I'm pretty confident I've been dealing with a miss all along, because it is the same symptoms, but happens at a lower rpm, and more violent, like more than 1 cylinder now. I'm thinking swap the plugs again for Iridiums and retest. I didn't put a FP regulator in yet cuz a guy I talked to said if they go bad its because it allows fuel to pass through when it shouldn't - floods out after hot soak. So if its starving for fuel, then it could be a fuel pump perhaps. Need a better scan tool. The old wires were basically welded to the plugs on the rear bank, what a pain. But get this, the new wire resistance was actually higher than the old ones I took out. If the old one was 300ohms, the new one was 600ohms. The old plugs looked barely used and still gap out at .060, but the shanks are well rusted. I'll see if Napa will let me defect out the DP'* and pay the difference for the Iridiums.

What'* your fuel pressure?

What oil are you running?