Trouble Codes/rough Idle

I Put A New Head Gasket And Timing Belt On My Girlfriends Car 97 Gs And Know It Idles Rough But Runs Great At Rpms Above 1000. It Has Trouble Codes 12 31 55 All Are Sensor Fault Codes. I Have A Hard Time Belivieng That All Three Of These Sensors Went Bad By Changing The Head Gasket, Any Ides On What Could Be Causing These Codes To Trip Out Would Be A Great Help, Thanks
(the Codes Are Knock Sensor Fault, Airflow Sensor Fault, Idle Air Control Sensor Fault)

Did you take any of the sensors out? Maybe it is just one wire or something that is not connected that is messing with the sensors and throwing the codes.

I Never Removed The Sensors But I Did Unplug Them To Take The Head Off. I Checked All Connections And They Seem To Be Good.

ok first off dont type with the CAPs lock on! its annoying to read a post with the first letter of every work capitalized!

now for the problem...
are you sure timing is correct! 420a motors are gay as hell to set timing on! and it sounds like your timing might be off one tooth, not enough to do major damage yet but in the long run you will start bending valves, if it is rev'd high! go to autozone and have them clear all the codes and see if they come back! if they do then start looking for other problems!

When I rebuilt my 420A I had the same problem. Come to find out that the timing was the problem. What I did to reset the codes is disconnect the battery for a while then reconnect it. Try that it may work. It's probably timing.