1997 honda civic dx. Engine starts normal, runs normal until it gets warmed up. Then the idle begins to fluctuate, surge or erractic. It gose from low idle (normal ) up to a high idle ( not normal ) then back to low idle then high idle.

 

https://www.hondacivicforum.com/m_351738/tm.htm

 

check the o2 sensor, same thing happened to mine

 

did you have a CEL.
he does not mention that

 

its your IACV, my car did the same thing. It's located on the back of your intake manifold and theirs 2 bolts, take them off and 2 hoses take them off then near the bottom theirs 3 phillip screws to unscrew, and a clip and take that off and it will come off. Then you can clean it w/carb cleaner and put it back on or replace it. It's also good to check for vaccum leaks and break booster.

 

It was the IACV, I took it apart, cleaned it , reinstalled, problem fixed. Thanks for the information.