sounds like an air / vac leak.. either do a vac/pressure test and fix or do a AIV removal.
Plenty of guides about it. you could also do with giving it a full connector check and clean. Also check PTS voltage and adjust if required and check IAA unit. also plenty of info on the Oz site...( a bit closer to home for you... lol) [ www.pexcom.com.au/z32cms/ ]