Engine possibly TBI problem

[GLittler]

Ok this question has a bunch of back story to set up. Ok, about two months ago my dad was working on my brothers Carburator (Its really a Throttle Body Injector, but i like to call it a carburator) and he broke the Mixture Control Solenoid on both mine and his so we got two used ones from a junk yard. It seemed to work fine but a few weeks after that i suddenly got the Check engine light every once in a while. It happened at two diferent times. One was when I would be sitting at a stop light and my engine would start slow and would cyclycally increase to a violent shake then it would settle down and the Check engine light would come on. The second occassion on which this would do is when i'm going down the road and it would slightly hold back a bit and then go back to normal and i'd get the light again.
The problem that really worries me is a few weeks ago i pulled into work turned off the engine and a small puff of smoke came out of my car. I didn't have time to check it cause i was late for work as is. A week ago i ran a diagnostic on my car and it said that something was wrong with The Throttle Positioning sensor and the Mixture control Solenoid. So in an attempt to alleviate the problem i switched to my brothers TBI and for a few days it worked fine then two days ago I got one of each problem again. Today, after putting on a new CV Boot and took it around the block and turned it off and it smoked again, this time i found out it was coming from the TBI.
My question is what could be causing this?