So..... I couldn't access my mate's oscilloscope as it's wired into an installation and I couldn't get the car close enough! So we used a quality multi-meter and got results which were different to what VIDA says.
1. At ignition on the engine pad valve gets 12V
2. With the engine idling it gets 14V with the alternator charging
3. Above 1100rpm approx the voltage drops to 10V.
We hooked the pad valve up to 12V and it clicks as it should.
Our conclusion without a good reference point was that the PWM signal is probably working.
On one occasion during the test when turning the ignition on, we got zero volts at the plug but switching off and on again we got 12V. Maybe I've got a dodgy wire somewhere?
Yesterday leaving work again, pulling away the fault returned. I pulled over, restarted and everything was fine. Today before leaving work I turned the ignition on then off again then started the car. No fault and the car pulled well. I'm going to investigate the wiring next.
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