Thank you for your input. As I did not have O2 sensor warning light on, I never suspected it. During a warm-up, does this system run open loop?

In any event, it's worth a try.

Interestingly, it has been running like a champ since I filled it with premium and 2 ounces of Sta-Bil Marine formula a week ago. Car sat for a long time and I wonder it had a bad gas in the tank.