electrical fault dash symbol

gday guys, I have a 1990 mr2 with a second gen 3sgte.
my problem is that over the last 2 days I have had the electrical fault dash symbol consistently appear, the effects this is having on my car are very noticeable.
instead of hitting 9 pound of boost im only hitting 5 and the car is running like a piece of shyte.
the diagnostic throw out 2 faults and they are ignition starter and knock sensor, my mechanic seems to think it may be the computer because 2 faults are popping up...
ive had a look at the connections and they are very clean. there were a few prongs that had the tiniest bit of corrosion but I cleaned them and still no good.
if I turn the car on after its been sitting for a while the fault does not appear on the dash until I start driving.. sometimes it comes on after 10 metres sometimes 50 metres, but no more then that. any help will be appreciated. sorry for the novel guys. cheers.
p.s ive also tried d/c the battery over night and tried in the morning, still no good cheers