My theory is a lot of it has to do with not having a MAF sensor as in later cars. Without a MAF, the ECU really has no idea how much air is coming in. The TPS plays a big part, but IMO the ambient air sensor plays a big part too in these special cases because the temp of the air is equally important.
I am going to spend some time experimenting with the ambient air sensor…i’m thinking of relocating it outside of the air cleaner. I seem to get better idling in the morning when the outside temperatures are much cooler, plus no bog when flooring it before the engine has fully warmed up. I know the ambient air sensor is a minor ECU trim adjustment, but it’s enough where if I pull it when the engine is warm, idle goes up quite a bit (too rich), and if I try to start it with it off once warmed up, it won’t start (too rich). With it pulled, there is infinite resistance, so the ECU thinks it’s pulling air from the north pole.
I’ve opened up my air intakes with the 2" PVC mod, but haven’t fitted cold air intake yet. My theory is that the air cleaner compartment (where I’ve relocated the ambient sensor because of my mod) eventually bakes under the hood, and sucks down very hot engine compartment air while idling, and can’t be cooled quickly with cool morning air while cruising. So I believe the ambient sensor is reporting temps higher than the air really is, thus leaning the fuel a tiny bit?
My infrared showed the air cleaner interior to be 150F. Ambient air was 75F. Engine compartment air was about 90F. Sender was reporting 780ohms (about 125-130F?)
One day I really need to fit a cold air intake so cooler air is always entering the air intake housing to help cool it. But for now I’m going to move it out of the air cleaner so it doesn’t get influenced by the air cleaner temps, AND I’m thinking of putting in a 100 ohm or even 200 ohm resistor so that the ambient sensor reports temps back about 20F cooler than it’s sensing, just to push things a tiny bit rich.
We shall see…