Most of the times this situation is because of uncalibrated TPS and some times coz of IACV but since in your case its fine on Petrol and there is no haunting idling issue, hesitation, surge, or hiccups at certain rpms- we'll narrow it down to the Advancer then.
Do you have the green advancer/emulator installed, called the 'New CIP 4'?
With the car idling, look at the bottom of the advancer. There should be one or more green lights. If there is a red light instead, your advancer's potentiometer needs adjustment.
There is a very good write up, on how to adjust it, by this worthy fellow here: