pbridges

Hi, I'm new to this forum. I've got a 99 Outback Legacy that has 180,500 miles on it. This is the second time the check engine light has come on. When I started the car it rev'd really high (around 2,000 RPM) and stayed there. This is on an automatic. That's when I noticed the check engine light was on. I put it in gear and drove it and it felt like it was going to stall out (it didn't but it felt like it would). Last time this happened it was the O2 sensor. Any ideas about whether I need to go to the dealer ASAP?