There's a ghost in my car!

[amoparman]

I have a problem with my wife's 90 shadow. The thing revs up by itself! I'll be driving along and pull into a gas station and when I put it in park it will idle for a minute then rev up like some one is doing it on purpose. It does not do it all the time maby once or twice a week. It doesn't seem to make a difference if it is warmed up or cold becuase it some times does it in the morning or half way throgh a drive but only when Im idleing in park. I had the thing idleing in the driveway after changing the oil went in side for a minute and heard the thing rev up and down came outside to see who was screwing with me and the car was empty. I changed the o2 sensor on it. The car was originaly a 2.5 and I replaced it with a 2.2 . But that was a year ago and this is the first time I have this problem Also when the car warms up and is going down the road at highway speeds it smells like rotten eggs bad. Is this the cat? I pulled the codes out of it with the keyswitch and it said battery disconnect with in last some odd key ons, and a every thing is normal code. I cant remember if I had the battery disconnected lataly or not. This is a tbi system.
Any one know where this ghost is? Suggestions?