2001 Ford Escort iM scared I bought a lemon

Shakes or Wobbles problem
2001 Ford Escort All Wheel Drive Automatic 68,000 miles

Ok, so I recently purchased a 2001 ford escort, 4 door. About a week into owning the car I was at the stop light and it just shut off, the dash was still on and radio was still running but the engine was out. So I shut off the car, put it into park, and restarted it and it turned right on. Since then it has been a normal thing, its literally a 50/50 shot at every light, the only way to ensure it doesnt shut off is that I leave space for me to slowly scoot forward until the light turns. My second problem is that the car idols. And it does it bad, so much everything in the car will shake. When it starts to idol really bad, then it shuts off. Also if the car is left on and in park the idoling gets worse, then it shuts off too. My last issue is, on and off when I turn the car on the dash will start blinking nonstop for like 5 minutes, and there will be a clicking sound. I was told this may be a warning sign, I assumed maybe it was cause my front right light keeps going in and out. (Sometimes it works, sometimes it doesnt) I took my car to the dealership and they said they hooked it up to the computer and found nothing wrong, he cleaned the idoling something (sorry im bad with cars) and it stopped stalling for like 2 weeks. He said the idoling he thought was because the previous owner installed a gas saving devise in the car, I dont know, I went with it because I dont know better, but that doesnt sound right. What do I need to do to fix my issues?