Vtec will not kick in with the CEL light on. The coolant temperature sensor is located near the vtec oil pressure switch, a little below the distributor. It has a single wire sensor plugged into it. Replace that sensor, fix your iacv(or replace), and replace your o2 and your car should work fine. Even if your CEL is off, vtec will not engage if your ecu has codes in it, so make sure you reset your ecu after you're done.