furry, If it does it in two cars then it could be any of the following....

1) Wired up wrong.
2) Faulty monitor loom.
3) Faulty monitor module.

Here is a wiring checklist just in case .....

CONNECTOR 1 PIN 1 - ECU PIN 15- WHITE WIRE - MAP SENSOR
CONNECTOR 1 PIN 2 - ECU PIN 31 - YELLOW WIRE - CHARGE AIR TEMPERATURE SENSOR
CONNECTOR 1 PIN 3 - ECU PIN 29 - BLUE WIRE - COOLANT TEMPERATURE SENSOR
CONNECTOR 1 PIN 4 - ECU PIN 17 - GREEN WIRE - THROTTLE POSITION SENSOR
CONNECTOR 1 PIN 5 - ECU PIN 25 - GREY WIRE - ECU IGNITION SIGNAL INPUT (IF FITTED)
CONNECTOR 1 PIN 6 - NOT USED
CONNECTOR 1 PIN 7 - ECU PIN 20 - RED WIRE - 12 VOLT POSITIVE SUPPLY
CONNECTOR 1 PIN 8 - ECU PIN 1 or 19 - BLACK WIRE - GROUND

This assumes the secs loom is the original one supplied of course