1992 Grand Prix 3.4L V6 DOHC high engine idle at cold start

[melissa_sj]

I am having trouble with the car at start up when the engine is cold. The rpms go to around 22-2500 then slowly come down, very slowly, about 10 to 15 minutes to get down to the normal 900rpms. The car only has about 87,000 miles, and I've replaced tons of stuff over the 8 years I've had it.
The car is a 5 speed, and I have recently replaced the clutch, drive belt (2nd time) and cam belt. Unfortunately the cam belt broke before I had it replaced. They said there was no visible damage, and the idle problem was occuring prior to the belt breaking. It has just gotten much worse over time, in that it takes longer and longer to idle down. The postings about idle issues don't sound exactly like what my car is doing, but could the gaskets be my problem also? I borrowed an autoxray scanner from a coworker and it gave me a trouble code "35 high engine idle error." The manual didn't have codes so I went to the manufacturers web site but there is nothing there about what 35 refers to, and high engine idle error doesn't come up either. The service engine soon light also comes on and off when the rpms occasionally spike during this long warm up period. I replaced the IAC, but that did nothing. Should I try the oxygen sensor before I go to the expense of having those gaskets replaced. I'm kinda nervous about trying that myself. The scan tool showed the oxygen sensor was okay, but it does show frequent fluctuations from running rich to lean. I read something about that having to do with the oxygen sensor, I think, in an earlier post. I am not good at diagnosing things, obviously, but am capable of replacing some things with the manual in hand. The check gauges light is on and off almost all the time now, but the gauges all look normal. I also occasionally have the anti lock light coming on, the fuse blew once, replaced that, hoping the light wouldn't come on again, but it still does. Any help would be greatly appreciated.
Thanks