Hyundai Repair: Is it there fault?, throttle position sensor, hyundai accent

Question
I have a 2001 Hyundai accent.I have to pass an emissions test so I took it to a shop.When they ran the test they said a code came up saying I needed a new throttle position sensor. (code p0121) So I told them to put a new one on. When I picked it up and tried to back up it would hardly move.So I went inside and told them and they said let it idle for about 5 min. and it might start working. So I did and when I left the parking lot it wouldn't go over 20mph. It stayed that way all the way home.So the next day I took it back to the shop and had them put my old one back on.They did, and when I left the parking lot it was still not running correctly. I could not get up passed 30mph. My car wasn't running great when I went there but it could go on a highway! So my question is can changing a throttle position sensor cause this. Could they be doing something wrong when they put it on?

Answer
Hello elaine,
A faulty throttle position sensor can cause all these problems. Did they replace it with a original/good part? Maybe they installed a bad sensor. Maybe they damaged the adjustment on the accelarator cable. There are a lot of possibilities. I think you need to go back there and tell them that they need to fix your car or at least bring it to the former condition.