Low idle engine stalls sometimes

Engine Performance problem 4 cyl Front Wheel Drive Automatic 44000 miles

My wife has a 2002 Volvo S40. Yesterday when starting the car, I noticed the engine idling very low and and unevenly while the car was still in Park. Once we began driving, the car ran fine with no obvious symptoms. The next time we started the car, however, the check engine light was on, but this time the engine did not idle low. It seemed normal. We drove on the interstate for around two hours with no issues and stopped for gas. I started the car back up and it was in Park for around 20 seconds and eventually began idling down and then died. I restarted the car but definitely noticed the engine not wanting to turn over right away. I gently tapped the accelerator and that seemed to help it. I pulled off and the car ran like normal for the remainder of our trip. I also do not notice any idling issues with the engine when I'm in Drive but stuck in slow/stop and go traffic. The problem only seems to happen when the car is in Park.

Any thoughts on these symptoms? Thanks.