There was a known problem with some small turbo escort cosworths with regards
the MAP sensor wiring.
This problem was high lighted on some standard cars but mainly on chipped cars.

Not all cars showed up this problem and it may now be showing up.
Please get a proper fault code/diagnostic done before doing this if NOT already done.

Usually when GGR convert a car themselves, they change this wire and it was
a known problem with ford as they have a finis code for the replacment sub loom.
(dont ask me what it is - talk to Alistair Mayne @ GGR)
This loom consists of a seperate 3 wire loom from the map sensor to the ecu
connector socket. This was usually incorporated into the main loom and
will be hard for non experienced persons to actually see if it has been fitted.



*** EDITED ***

Also checked the multiplugs on the inner wing are in good condition and
do not have water or corrosion in them.

Just another suggestion