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]

I spent some time playing with the car this afternoon -- I backed it out of the garage and worked on it in the driveway.

I checked the timing, and it was about a degree advanced, but it wasn't off much. Just to confirm my process:

• I removed the vacuum hose from the throttle body and plugged the port.
• Then, I had my wife rev the engine to 3500 RPM and hold it there.
• Then, I set the timing light to 27 degrees and turned the distributor until the "0" on the cooling fan showed in the notch inside the shroud.
• Afterwards, I locked down the distributor, reconnected the vacuum hose and reinstalled the plug on the cooling shroud.

And so, the car was back to idling happily at 1600-ish RPM. I pulled the small vacuum line off the decel valve and hooked up my tested vacuum gauge, and it showed about 10" of vacuum. I slowly started turning in the idle bleed screw to bring down the RPM. I got it down to 1050-1100 and it was pretty stable, but idling at 7"-8" of vacuum, which just seems low.

At this point, I buttoned everything back up and took it for a quick test drive. Got about 1/2 mile down the road to the first stop light, and the car was idling at 1600 RPM again. I didn't change anything! Drove for a couple more miles and went home, but idle stayed at 1600-ish. I had a little bit of light-throttle stumbling at 2100-2300 RPM, but otherwise the engine felt good and ran well.

I don't know. I can make the car stall by closing the idle bleed valve, so there aren't any huge vacuum leaks. And, as the idle slows, the vacuum gets less (i.e., gets closer to atmospheric) whereas I would have expected it to get higher (i.e., closer to perfect vacuum). I'm still wondering if it's the cam, since too much overlap could explain the low vacuum at low RPM.