1997 Sunfire 2.2l. Having some weird problems with the Sunfire that just developed a few weeks ago. On a cold start the car is great, fires right up and feels good. However, if I’m driving, then stop to grab lunch or something, when I come back the car stumbles and stutters. I can smell gas for a bit, about 10 seconds, then it evens back out and runs great. If I let the car completely cool, then it starts fine, and if I just stop for gas then it’s fine. But over like 5 minutes then it stumbles for 10-12 seconds. Any ideas?

I had a very similar problem on my 1996 2.4L. The coolant temperature sensor (not the thermostat) was providing inaccurate, too-cold temperature readings to the car's computer, so the car's computer constantly provided a rich fuel mixture to the engine. That rich fuel mixture was good when the engine was cold but too-rich after the engine warmed up. (If you're an old fart like me, you may recall that in the pre-computer-car days, you had to manually engage the choke to provide a richer fuel mixture when the car was cold but then the choke had to be disengaged when the car warmed up or it would run poorly. Computers do that automatically nowadays.) Replacing the coolant temperature sensor solved my problem.

Apparently, it's difficult to test the sensor itself but the sensors are cheap ($5-$18) and easy to (do-it-yourself) replace so it's not worth testing if you think there's a good chance it's the problem. For your 1996 2.2L, I think it would be the AC Delco part # 1551107 or equivalent.

Here's a how-to video link...
https://www.youtube.com/watch?v=ShLu0nAd2AY

Please let us know how thing turn out.