D-jet idle and lean issues. Options

[Literati914]

1.7 w/ original D-jet.

I have the idle screw on the TB cranked all the way down/closed (which doesn't seem right tbh) and the car's idleing around 900rpm - which is within the recommended 850+/- , and the idle does not really "surge" too much but is not necessarily rock steady either. I'm also getting a steady 16.5 A/F on my gauge during idle and warm driving. So too lean. BTW, the CHT gauge has never gotten over 300 so it's not trying to over heat.

I'll be spraying the vacuum connections to see if I can find leaks - but other than that, what would be the most obvious culprit(s)?

My theory is that the idle screw needing to be closed (for a reasonable idle) is just combating say, a bad AAR or something. Sound logical? What tests can I do to the AAR or other items to look at first?

[Literati914]

My ‘72 has the idle mixture knob on the ECU.

Well, you could richen it with that. I suspect as the engine ages it probably has different requirements from when it left the factory. Have you tried some PEA fuel system cleaner? Like the 10$ gumout stuff? Maybe your injectors are getting gummy. A lean mix is gonna play havoc with idle, could be as simple as a bad tank of gas....

Yes like @Ishley confirmed, my '72 also has the knob - it does not "seem" to do much of anything to the idle though ... actually I'm not sensing any clicks from it like you are supposed to (maybe the knob's receiver hole is worn out). I will go back and examine that for sure though. I moved it CW while engine was running and watching the gauge and there was no change at all. But besides, the gauge NEVER shows anything but 16.5 even when out hustling it around the neighborhood - and the knob is only for idle (so I admittedly put little importance on it as being the root cause of the lean gauge numbers).

I have not used any injector cleaner - but gummy or clog(ging) injectors are possible as I've had to clean the fuel filter twice now from a buzzing fuel pump. My tank clean before install obviously left rust-dust particles behind. The pump is quiet after the filter clean and the car runs with plenty of pep - pulls surprisingly well tbh. I've purposely left the fuel level low to help evacuate remaining rust micro particles. I wish the bottom of the tank was ever-so-slightly funneled to the output fitting.

Oh, I did raise by fuel pressure from 27-28 to 30psi, which helped smooth idle but did not richen my mixture, according to the gauge.