after some testing, I could see there was a short coming from the MAP sensor. decided to get a new loom. while disconnecting the old loom, I noticed a bent pin in the big square connector, sure enough the one from the map sensor was shorting out agains the +5v supply to the sensor. (pin 13, bent into pin 12)
. straightened the pin, reconnected. We could see a dodgy repair on the old loom too, so took the plunger and swapped it out.
BINGO!! 12 months of very ropey driving, and she's purring like a kitten...