• Have a Honda civic (1.5 L) , 5 speed with the following problem: After engine warms up, while in neutral, idle speed bogs down then back up but no power is lost on any of gear shifting.
  
• It does lose power going down the road. But if i give it a little gas
• it will keep going.
• Could it be the oxygen sensor?

. Clean the Idle Air Control Valve (IACV), throttle body, and upper and lower ports.
. Replace the Ignition Control Valve (ICM), if the problem persists. This is the ideal time to also replace the coil and rotor, since you'll have the distributor open.