What do I do with my car?

As some of you know, I have been having problems with my car. My car shakes or vibrates violently when on idle. That is, when I approach a stop sign or a four-way intersection, it starts shaking and I normally end up shifting to neutral and wait for the signal to turn green before I drive normally again. A Mitsubishi dealer diagnosed the problem as a faulty EGR valve and so I had it ordered and replaced by another auto body shop but the problem still persisted. Tired of this happening often and after having discussions with others, I decided to buy a new car. I check out the Toyota Prius synergy drive hybrid car. It is a "cute" car which doesn't feel like one when you are inside and doesn't look like one either from outside. I liked it very much and decided to pay a down payment for one either this weekend or the Monday after that because, the car is usually not readily available with any dealer. The irony is that my car, the one that I have now, seems to want to run normally again. There is no weird shaking or vibration when I stop and the car runs smoother than ever. What do I do with it?