My 01 Santa Fe has had a problem with engine hesitation since I bought it two years ago. At first it was barely noticeable but now is terrible. I have had it in garage several times. Computer said it was mass air sensor so that was changed, then engine light came back on and engine did same thing. Then computer said O2 sensor so that was changed. Didn't help. I had spark plugs changed recently and it helped some but the mechanic that worked on it said they don't usually work on foreign cars there and he only did it as a favor when he changed my tires because it was so jerky. He also said it seems to do this hesitating/jerking thing when it downshifts. Anyone out there had similar problems and know what it wrong?? I have spent mucho dollars on this vehicle and can't afford to keep dumping money into it as I am a single disabled Mom on child support and alimony. Not a lot of money to spend. I am getting a tax return next week and want to get it fixed right. If I had a clue as to what it wrong with it maybe my money will finally be well spent. It also squeals once in awhile when it's cold and I start it up. It acts up worse when it's cold. PLEASE HELP ME, ALL YOU MECHANIC GUYS OUT THERE!