blues2k3

I have a F20c turbo that is having intermittent problems with vtec engagement. When the motor is cold I get two or three passes on the dyno where vtec does engage. Once the car is warm the vtec then becomes inconsistent. I watched the oil pressure on each run and it remains the same at 80psi and goes up a bit. I cleaned the vtec screen a few times and also did some oil changes attempting to isolate the problem. Oil level is perfect and full. The solenoid was also tested electrically with a trigger wire and it does engage fine when manually triggered. I am using AEM also. Any thoughts? thanks