The afm flap should definitely be open slightly at idle as toyotec has said..... If anything, it sounds like the tension in the flap spring may have been slack allowing it to open too far at idle and causing the rich mixture..... Id try setting the idle mixture with the top off the afm so you can see what is happening. Where the flap sits at idle directly relates to how the ecu will fuel the engine... Adjusting the toothed black wheel to add spring tension should add more closed bias to the flap and enable you to adjust the idle CO using the bypass screw
Hi all. I know how annoying it is when you don't know if the car is fixed and what fixed it, so here you are. It was the AFM, I did as a couple of you said and adjusted the spring tension on the flap, 3 notches in the end. The CO is now about 1.8%. You can tell if the spring is weak by running the car at idle, with the top removed from the AFM and watching the track arm. If it bounces about the spring is weak, tightening the spring makes it very steady. The car drives well and hopefully I'll save some fuel now. Many thanks for all your input , it's very much appreciated.
does adjusting the spring tension affect the fuelling above idle? I figure that it must, in that with a tighter AFM spring the AFM flap will be less open than it would otherwise be, and so injector duration will be less.... therefore there must be a risk of underfuelling, so how do you guage how much to tighten the spring??! (by tightening the spring I think the plan is to correct a weakened spring, ie to get back to "factory" and compensate for spring fatigue over the years)
Yeah it probably does effect the fueling but it was probably over fueling through the whole rev. range anyway. The car drives fine and if it was under fueling I'd expect lack of power and misfiring. Only time will tell, it's twenty two years old now so I can't complain that it's getting a bit tired!
