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.

[Superhawk996]

Pull plugs - betting they are black given how little vacuum you have . Post photos of plugs.

Likewise if you want you can put a mighty vac on the MPS and pull vacuum and and see if that helps allow you to better use the air bleed screw to bring RPMs down without the stalling. Will help narrow down whether it’s the lack of vacuum causing issues or something else.


Those numbers are so low I almost question the vacuum gauge.

[BillC]

Pull plugs - betting they are black given how little vacuum you have . Post photos of plugs.

Likewise if you want you can put a mighty vac on the MPS and pull vacuum and and see if that helps allow you to better use the air bleed screw to bring RPMs down without the stalling. Will help narrow down whether it’s the lack of vacuum causing issues or something else.


Those numbers are so low I almost question the vacuum gauge.

I had pulled a plug the other day, when I replaced the CHT. The center electrode was a medium brown color. Not going to bother pulling any of the other plugs until I get further along with the diagnosis -- the car is definitely running rich when I try to make it idle where it should, so the plugs won't tell us anything new. And, that richness is almost definitely because the vacuum level is so low.

I did hook up my old mityvac to the vacuum gauge I used yesterday, and it turns out the vacuum gauge is toast. The needle stops at 11", and between 0 and 11 it reads about half the mityvac. <sigh> Now I have to get another gauge.... However, even with the bad gauge, we know the vacuum is low -- that needle should have been pegged at the gauge's maximum the whole time the car was idling.

I did call the shop that rebuilt the engine. They actually remembered the PO ("That's a name we haven't heard in a while."), not sure if that's good or bad.... They are going to look up the build information and will give me a call back about the cam.