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 finally heard back from the shop that built the engine. They left a message on my phone that said they put a web-cam 110 in the engine.

I checked WebCam's web site, and didn't find a 110-grind cam under the Type 4 listings. So then I called WebCam, and they confirmed that they don't sell (and never have sold) a 110 grind for the Type 4 engine.

Unfortunately, when I called the shop back, the builder had already left for the weekend. I left a message, but probably won't hear back before Monday.

I did check WebCam's listing for Type 4 cams that come close to the 110 specs, and I'm wondering if they put an 86a cam inside.

Either way, the specs are wrong. An Engle 110 has 31 degrees overlap, a WebCam 110 is 39 degrees, and a WebCam 86a is 35 degrees. Stock cam (according to WebCam's website) is 8 degrees overlap.

I'm guessing the shop that built the engine thought the PO was going to convert to carbs, and/or the PO just didn't know any better.

Unless I get a call back next week with a different cam number, I think we now know why the vacuum is so low at idle.

Now I just need to figure out which way to go. I definitely don't want to downgrade to carbs. I also really don't want to have to replace the cam, since the engine was rebuilt only 300-500 miles ago, and it runs very strong over 2000 RPM. @JamesM has told me some enticing details about going MS3, so I'm waiting to hear back more from him about that option.

If I have a chance this weekend, I'll jack it back up and put a dial indicator on the rockers and directly measure the actual lift, to confirm one way or the other.

[JamesM]

Now I just need to figure out which way to go. I definitely don't want to downgrade to carbs. I also really don't want to have to replace the cam, since the engine was rebuilt only 300-500 miles ago, and it runs very strong over 2000 RPM. @JamesM has told me some enticing details about going MS3, so I'm waiting to hear back more from him about that option.

Just now seeing this thread.

My initial thought as to the high idle that dies when you close my brain immediately jumps to timing. To much advance kicks up the idle speed and by the time you close the bypass screw you have cut off to much air to keep it running.

The vac retard at idle normally pulls down the idle speed so would make sense that if you don't have proper vacuum its not pulling enough timing. Might be able to account for it with a different map on the 123 (or just manually cranking back the timing)

But with so many unknown variables I would say Megasquirt is the "Easy Button" though some custom tuning may be required to accommodate whatever this engine wants.


FYI one of my personal 914s with Megasquirt, big valve 2056 with an EMW "J" cam (307 duration) idles like stock ~900 rpm even with a highly lightened flywheel.

Stock idle RPM anyways, with the cam and headers it has a wonderful lump to it.
https://youtu.be/O5JkdbyhWMc