2002 Buick Lesabre Engine Stalling

My engine started stalling a couple of weeks ago.
I took it to a repair shop and he changed my spark plugs and wires. Also cleaned my injectors. About a week later the check engine light came on. I took it back to the shop and the code came up for the thermostat. At that time, the mechanic cleared the code and said he was not sure why it put that code out, to go ahead and drive it and if it came back on, bring it back to him. For a few weeks it never stalled. I started it up yesterday and could smell strong gas. It seemed to idle different (low) but I live in Ky and it is very cold right now. I drove it about a half mile and stopped at a stop sign. It stalled. I had to make three attempts to get it to start again. Over the last few weeks, it may run with no problems, then other days it stalls. I haven't been driving it much because I am afraid of breaking down. Please help me!