S16 Vacume Amplifier Solinoid Switch

[jerseypug 1]

just replaced the vacume amplifier on my s16 and the car runs great untill it has warmed up. it then looses power below 4000 revs. when it is cold and the engine is reved the 2 vacume arms that close the 4 inlet manifold ports close then open fine. when it is warm they dont move. is this likely to be the solonoid switch on its way out and playing up? does anyone know if the switch is controlled by the ecu?