sputters jerks feels like it will stall then picks right up new MAF no help on 2000 Toyota Echo

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i changed the spark plugs (original)120k changed MAF sensor i got a too rich code and low fuel code
if i drive up a hill it will downshift and engine purrs, but regular driving i get whiplash (like learning to drive a stick LOL) if you have an idea what i should check next i would appreciate it
(2) Answers
Ignition misfire, coil(s) spark plug(s) that's my guess. More pronounced in HIGH gear but dont feel it when it downshifts to a lower gear!
I had same problem,I changed - MAF, 4 coils, spark plugs, oil, air filter, COMPUTER, cleaned air intake, car still acting the same, finally it died all together, none of this did any help, no change, THEN car died, would not run, changed fuel pump, started but not running good, took fuel pump out ( only 21 psi) changed fuel filter, not screen at bottom, but, fuel filter, yes taking fuel pump appart again, WOW passed several cars on highway, 145km/hr, stops, starts, almost squeels tires. LOL,,, and 45 miles yes miles to the gallon, good luck , test pump for pressure, look in tank for dirt, if you find dirt clean it out, drain tank, then look to see how dirt is getting into tank, after you change fuel pump and filter, should be around 55 psi+