light load surge finally nailed

[fasterfaster]

Rb I think your chasing the prob in the wrong area.......... from info you have given symptons are more prone to be occuring at light throttle settings which to me is indicating fuel delivery or mapping fault.
Odds on it's running to lean at light throttle and the motor is "hunting" which is creating the surge effect.
Also check TPS setting (with a volt meter)
Just my .0000001 cents worth