I've been doing some reading and speaking to a mechanic trying to diagnose a hesitation and rough idling issue. I think I've ruled out a vacuum leak by spraying flammable gas around the seals and not noticing any change in behaviour. I'm seeing low manifold pressure with the scan tool (around 27 - 37 kPa vs expected range of 64 - 69 kPa) and the mechanic thinks that as long as there isn't a vacuum leak, this is probably related to valves. Obviously a vacuum leak is the faster and cheaper thing to rule out, but since it's been mentioned I'm also just curious - is it even possible for a vacuum leak to be the cause of a drop in MAP? I would have thought with more air coming in through the leak, pressure would increase.
The motor is a 2.3l Duratec HE petrol I4, non turbo, in a 2010 Ford Transit.