Car shakes, turns off and several warning lights turn on

I have a 2016 scion iA. I bought it as a lemon car. It started to give me issues before I even drove it for 2,000 miles. It has been in the shop for more than four times for this issue, once for several months. When purchased I was told of the issue that the car had (yeah. Shaking), but that it was fixed and was also under warranty and that all parts were replaced with original parts and the issue would not come back. Long story short, I contacted Toyota financial and took the car to the Toyota dealer, I was told that there was no problem with the car but Toyota financial wanted the mechanics to perform some tests. I was then contacted and told that there was excessive carbon build up in the engine but that this was not related to the shaking, past issue. I do want to return the vehicle because at this point I have had it with taking the car to the shop. Question here is, is it normal for a car to get excessive carbon build up? Is it related to the shaking of the car? Previous code cas p210100? Also, I purchased the car in 2017 with 11,680 miles, now it has 25,503.