Rough Idle, Stall problem...repairs not helping

Hope U got it fixed by now. Around those miles my car would stall and the dealer replaced a bunch on belts and stuff, thank god it was still under warranty. Now my 02 Sonata has 80K miles and I have all the symptoms you have. Rough idle; I have a voltage meter on my stereo and see it drop when it shakes. It actually turned off once @ a stop. Had the battery tested @ Autozone...it checked ok. Took it to local shop for another issue (leaking boot). They said it had a transmission code and that the dealer should know what it is. The dealer kept the car for 2 days and basically said their hands were tied w/o a code. They did suggest that it could be the alternator (since I have HID lights and sound system). Can't believe they couldn't fix it. The car continued to shake during stops. Leaving the radio off did help, but just seem to prolong not fix the problem. Actually turned off on me twice today (both while traveling @ slow speeds). A co-worker of mine has a cousin that worked for Hyundai and he suggested to replace the Throttle Position Sensor. It's less that $50. I will try this tomorrow and post what happens. ***Well took me for ever to reply, but the Throttle Position Sensor made the car run better only in my head. It didn't help at all. The check engine light finally came on again, took it to the dealer. Told me I needed a new transmission. Told them great, change it....they replied it be $1700. I told them it was still under warranty. Then they checked it further and it was the the EGR valve, again, but this time it was no longer under warranty. So I still ended up paying over $1K. Now 3 years later and my car has almost 120K miles and it's been acting up again. Haven't turned off on me yet, but I know its a matter of time.