so why is there an earth on one of the bolt holes?

seen this about 20 times on rally cars that have had the sensor cable tied to the strut brace with no earth,missfire and behave exactly as paul describes above,change the sensor,add an earth and problem solved.

of course iam not saying that this is the problem here,just offering advice based 100% on experience of cosworths i have had over the past 18 years rallying them.maybe rally cars are different but boreham earthed all their map sensors on a seperate earth.