Idle adjustment question, Idles high or slowly stalls Options

[BillC]

I have an idle adjustment question for all you D-Jet gurus:

I can adjust the idle air screw on the throttle body so the car idles at 1600 RPM, and it will happily idle at 1600 all day long. If I turn in the screw just a little bit, like 1/4 turn, the car will slowly drop idle speed down slower and slower until it stalls. I can blip the throttle to keep it running, but it just wants to slow down and stall. This is all when the car is fully warmed up.

How do I get the car to idle steady around 1000-1200 RPM? 1600 is just too high.

Car is a '73 2.0 with factory D-Jet. I installed new Standard Products FJ67 injectors, and the fuel pressure is 29 psi. There are no leaks in the intake side, and the idle adjustment screw is about 2 turns out (so there's plenty of adjustment available in both directions). The MPS hasn't been messed with, and the ECU looks like the correct unit. All new vacuum lines, fuel lines, pump & filter, and fresh gas. New @JeffBowlsby engine and alternator wiring harnesses.

Known issues: it has the wrong CHT sensor (it's the one that's commonly available) and I think the TPS board has worn traces. I finally found the right CHT and ballast resistor, and I also have a 914Rubber replacement TPS board, and I will install both of them when I get a chance. However, I don't think either of those should keep it from idling at a reasonable RPM.

[BillC]

Aarrrrrgggh!!!! It is not fixed. (IMG:style_emoticons/default/headbang.gif) (IMG:style_emoticons/default/headbang.gif) (IMG:style_emoticons/default/headbang.gif)

Took it for a test drive, and drivability is definitely improved. However, it is still doing the idle-at-1600-or-drop-down-and-stall thing. Doesn't matter how much I play with the idle bleed screw and/or the ECU knob, it wants to stay at 1600 RPM or it will slowly drop down and stall.

With it idling at 1600, I can start making slow tweeks to close the idle bleed screw -- turning maybe 5 degrees at a time, it will be turn/wait/no-change, for multiple repetitions, then after the 7th or 8th tweek, the RPM will start coming down and it will stall. Sometimes it will seem to stabilize around 1000-1100, but it will proceed to stall after a minute or two.

It acts like something is leaking a little bit of air at 1600 RPM, but slowly closes off when the idle drops, to the point where it stops adding the supplemental air and the car stalls. I can try smoke-testing it again, but this only seems to show under vacuum, not under pressure from the smoke machine.

I thought maybe the PCV valve was acting up. It is, after all, 50+ years old. So I disconnected the hose from the manifold and plugged the port. I had to open the idle bleed screw most of a turn before the car would idle, but then it was stable (again) at 1600. And, as I closed the bleed screw in small, slow steps, it would do the same thing, only much slower down the slope to stalling.

One thing I noticed is that at higher RPM (1300 and up), there was nothing visible coming from the open end of the PCV hose, and no pressure/vacuum felt when I put my thumb over the end. But, when the RPM dropped down to 1000-1100, I could see a very faint trace of smoke from the hose. If I blipped the throttle, the smoke would disappear until RPM dropped back down to 1000-1100.

The previous owner had the engine rebuilt a year before I bought the car. And, I have installed all new vacuum hoses and rubber fittings. I also smoke tested the intake system previously, and there are no leaks except a very small amount around both ends the throttle shaft. I have confirmed that the ECU, MPS and CHT with ballast resistor are all correct for the car.

I am very frustrated. My old 1.7 idled rock-solid at 900 RPM, so I know the D-Jet can behave like it is supposed to.
Any more suggestions?

Edit: additional info: Distributor is a new 123Ignition unit. Along with the new hoses and injectors, I also installed new spark plugs and new ignition wires.