I was having the same issue along with many others on a CS 1.6 Server and we were assuming it was more issues due to a recent string of DDoS attacks on that servers host, but now I'm wondering if the issue was steam related. When I was having the issue yesterday it would start to settle back down to normal after about an hour of playing on that server. I didn't try testing it out but I'm assuming disconnecting and reconnecting would have put my ping back up where it was. If you like to play on the same server for long periods of time just try toughing it out for a bit and see if your ping starts to "settle" after a while.