Hoooray! Another intermittent wiring fault =(

[Colza]

This morning i started the car up, and for some reason the boost-whatever-it-does solenoid was going absolutely mental. My 'black box' is in the windscreen wiper motor cavity and normally there is a 'knock' when ever the car goes from vacuum to boost as it switches whatever it switches. For the whole of today whenever the car has been cold it has been switching so fast it goes 'RARAAAAAAAAAAAARRR' until you drive off, and it goes back to being normal. Havent noticed any other differences, no error codes or anything.
Any ideas?

Also later this arvo it coughed up an error 5 which it used to do all the time thanks to some dodge wiring around the MAP sensors. I fixed that ages ago though :-/