My guess is either fuel starvation from a REALLY bad fuel filter, a weak main pump, or a dead in-tank pump- all of which ought to give low fuel pressure, which you can have tested...

OR... a bad air mass meter, on it's way out, dying, whatever. You can disconnect it (with the key OFF) and try running without it, and see if behavior changes. You'll probably get the Check Engine light all the time but the engine performance ought to be different, if this is contributing.

Good luck with it!
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Rob Bareiss, New London CT ::: Roterande Fläkt Och Drivremmar!