More than likely you've got a plug that is borderline. I've seen that before, time to test them. It may also be a bad temperature sensor, I know that on later cars the GP relay can also indicate a fault in a sensor.

__________________
Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC