1997 Grand Am Se 3100 surges then races then either dies or levels off

[Guldukat_dr]

I have a 1997 Pontiac Grand Am SE with a 3100 in it. At idle when you start it, it will idle fine and then start to surge. It will surge for a while and either die or race up to about 2000 rpm and then level off back at a good idle speed. If I try and move the car before it ever leveled off it will kick and sputter trying to move until I raise the RPM's up with the accelerator and then it will drive fine. I have replaced the IAC and the TPS on it. It does come up with code P0420 - Catalyst system efficiency below threshold (Bank 1). This occurs while driving on the highway or interstate. It never occurs at idle or in town driving. I am not sure if the two are related.

[Hoags]

It almost sounds like a vacuum issue, you may want to take a look at the vac. lines and connection points (splicers and/or tees). You should take a look at the EGR Valve.

Hope this helps.