kr isv problems

I have had my 16v caddy sport up and running for a while now without any problems apart from an annoying misfire at around 2500 rpm but recently my isv valve has been intermittently not working.  sometimes its silent when I go to start the car and the car idles very low. it all seems to be connected ok just wondering if it could be the coil or ignition switch playing up.

I think it was the coil from the donor car so should be the right one but had a new ign switch as mine burnt out. is there a way I can test them?

I have the isv powered from the coil if that makes any difference  

the isv is fed from the control box, maybe check the ignition live feed to it is good and the earth is clean. on the 16v it earths to the head, but it could be anywhere since its a converted car. its brown/white from isv box anyway

still having problems with this it is very strange as it will work sometimes and 30 seconds later it wont. gonna have to get a tester to see whats going on