Starts surging when it warms up to reg. Temp.

My 98 starts surging when it reaches regular operating temperature. When its cold it never surges. I can watch the temp gauge and tell you when its going to start surging. Changed plugs, O2 sensor, mass air flow sensor. Its been doing this for over a year. No error codes.......

My 98 starts surging when it reaches regular operating temperature. When its cold it never surges. I can watch the temp gauge and tell you when its going to start surging. Changed plugs, O2 sensor, mass air flow sensor. Its been doing this for over a year. No error codes.......
I just saw a reply for the same issue ( in the Cavalier section )and the person that had the problem checked the same thing but nothig was fixed . in the end someone told him to check the EGR . He changed it and fixed the problem. Try that it makes sense to me.