It's a VERY common fault on the EsCos for the main loom multi-plugs to corrode, esp. given where Ford positioned them - a common fix is to carefully cut out the corroded wire and make good, solder & heatshrink.

The Sapphire had these plugs on the bulkhead, at the back of the engine bay IIRC.

Basically, on my old Cos, just lifting the plugs up gently showed a massive temperature swing on the Pectel Monitor. ECU thinks charge air is very cold, it adds more fuel....

Is your loom standard from factory, or has loom been changed?