I've been messing with my V8 for a few weeks now, also has a simliar problem but im on LPG..... So far as I have a (or had) a complete car in spares as a donor that was a good runner, I have swapped out stepper motor,AFM,Thermo sensors, bought a complete Brand New Plenum chamber with all new butterfly mech on, that actually made a nice difference when I rebuilt all that lot and the old plenum was minging inside. However this idle problem remains except its not actually an idle problem really.... I start the car on petrol, blip the throttle and it switches to gas, I then have a nice solid idle of around 800-900rpm and then I select D or R and it drops to around 550-600rpm all OK its nice and solid and smooth. Then as im driving as I let off the throttle to roll up to a junction or a set of lights the rev counter goes right down to zero and the motor cuts out. It will start again no probs but its a pain as I have to start on Petrol and the fuel pump is currently on a manual switch that I have to engage to start up, blip the throttle then switch off again!
Anyone got any ideas on this one?
Cheers
PS Timing is correct for gas and I have not done the T-box oil, car has a genuine 87K on the clock.