I have a Volvo S60 2001 and ever since the winter came around it's been giving me trouble. When I start it up and it's in park it will sometimes start revving up the rpm. Sometimes it climbs to 3 or 4 thousand. Other time it will only go up to 2 or 2.5 thousand. And sometimes it will just start up and go straight to 1000 and shake and misfire. I've cleaned the throttle body, added coolant and checked the thermometer with an ohm reader. But it still acts weird about half the time. I really only get the issue when I'm in park after I just started it up. The car only has 100000 miles on it. A check engine light came on for a second then disappeared. The only code I could get out of it is P1620 and I can't find any good information on that code.
Any advise helps. Like I said, it still drives normal, I just hate starting it up because I never know what it is going to do.
Thanks!
also, this problem started after I took it in to the tire shop to get some new winter tires on it. I think they did some inspecting so maybe they bumped some wires or something.