A week ago I bought a Civic [D16Y8] and it seems when it gets warm it starts to hesitate while shifting through the gears. Best way I can explain it is if I was going about 20mph and in a high gear (like 4th or 5th), but it also seems that after a certain rpm (maybe about 2500/3000) it 'kicks' in and accelerates normal. Weird thing is, if I shut the car off and turn it back on it shifts like normal for a certain amount and time and goes back to the hesitation. I put in some NGK copper spark plugs and new wires, and cleaned the IACV. Where should I start?

 

that eliminates ignition. sounds like it runs right in open loop. i'd start with the primary o2. test.