1500 rpm under 25% throttle

I have a 2000 acura integra gs-r with the b18c1 engine. Its entirely stock besides DC 4-2-1 headers and a short ram intake. When warmed up i get a rpm surge at 1500 rpm’s in gear and in neutral under 20-25% throttle. This issue started recently after replacing my OBD2 P72 ecu with a OBD1 P72 ecu that is not chipped or modified. My previous ecu appeared to have had moisture in it and was pretty well corroded and had several capacitors blown out and leaking. The car wouldnt even run with that ecu. I swapped to the OBD1 ecu for 2 reasons, i could get the ecu on the spot and i dont live anywhere near a acura/honda dealership that could reprogram the immobilizer to work in my car with the OBD2 ecu nor could i afford to tow it there. This car is my daily and i cannot afford to miss work. I have replaced the IACV, throttle body gasket, Throttle position sensor, adjusted throttle cable not too tight, and checked multiple times for vacuum leaks which i know these would cause the issue. I for the life of me dont know what would cause this and would just like a second brain to help me think about what may cause this. I also would like to add that i doubt the ecu is the cause as it was running a 98 integra with the same engine and didnt have this concern. I dont know if this was happening with the original OBD2 ecu because i bought the car cheap. The previous owner couldnt get it running so sold it to me. The car runs amazing now except this issue and my car lacking a FITV so it doesnt idle high enough cold.