Very weird idle

[fwdturbobov1996]

CEL came on. Disconnected battery. Started it back up, idled at 100-200 wtf. Then went and drove it, came back, idled at 500. before I disconnected teh battery it idled at 900 to 1500. The CEL has not come back on. Any ideas. Cat? ICS? 1997 stock gs-t btw. 128k

 

[fwdturbobov1996]

Backed the ics all the way back out only raised the idle to 900. At 40 mph put in neutral car will go down to 1-200 rpm, come to a stop and will stay, then slowly make its way back up to 750 idle that I had it at. What is going on with this car. Everything is connected and sometimes there is a bad smell. Clogged cat is what I want to guess for the smell