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.

[emerygt350]

Did you check the timing when it was at 1600? If your weights are sticking you will see it far more advanced than it should be. The 10 is concerning.

I would:
1) check the timing when it sticks at 1600.
2) if the timing it not overly advanced (anyone know what it should be at 1600? I would guess somewhere around 17) than I would put the mighty vac on the mps and see how the engine reacts to 17inhg.
3) if that brings the idle down to where it should be (ish) than I would do a crusty style valve adjustment http://www.914world.com/bbs2/index.php?showtopic=28758

I would then check my vacuum again. If it's still at 10, compression and leak down?

This is all assuming the lift rules out the aggressive cam.

If you think it might be the aggressive cam, just pop the mightyvac on the mps, give it 17inhg or more and start the car. See if it idles where it should be.

[BillC]

Did you check the timing when it was at 1600? If your weights are sticking you will see it far more advanced than it should be. The 10 is concerning.

I would:
1) check the timing when it sticks at 1600.
2) if the timing it not overly advanced (anyone know what it should be at 1600? I would guess somewhere around 17) than I would put the mighty vac on the mps and see how the engine reacts to 17inhg.
3) if that brings the idle down to where it should be (ish) than I would do a crusty style valve adjustment http://www.914world.com/bbs2/index.php?showtopic=28758

I would then check my vacuum again. If it's still at 10, compression and leak down?

This is all assuming the lift rules out the aggressive cam.

If you think it might be the aggressive cam, just pop the mightyvac on the mps, give it 17inhg or more and start the car. See if it idles where it should be.

The distributor is a brand-new 123Ignition electronic distributor. So, no weights to stick.

I did a quick check of the valve adjustment while I was under there trying to measure valve lift. The valves were all fine.

I'll try a compression/leakdown check and then the MityVac on the MPS when I get a chance. But, it'll be next weekend at the earliest.

[Superhawk996]

I did a quick check of the valve adjustment while I was under there trying to measure valve lift. The valves were all fine.

I'll try a compression/leakdown check and then the MityVac on the MPS when I get a chance. But, it'll be next weekend at the earliest.

Don’t take this the wrong way but we recently had someone that was adjusting valves too tight causing starting & running issues due to low vacuum. Adjusting them so that only the slightest of drag is on the feeler gauge? Checking again after the jamb nut is tightened to ensure they didn’t tighten up when the jamb nut was tightened?

Compression and leak down are valid next step and will turn up issues if valves aren’t adjusted properly. Leak down would be preferred so you can narrow down the source of leakage. Leak down is another infrequently used specialty tool that not everyone has and takes a little practice to use properly so understand if that’s not an option.

[BillC]

Don’t take this the wrong way but we recently had someone that was adjusting valves too tight causing starting & running issues due to low vacuum. Adjusting them so that only the slightest of drag is on the feeler gauge? Checking again after the jamb nut is tightened to ensure they didn’t tighten up when the jamb nut was tightened?

Yes, and yes. I understand why you are asking, and it's good to check, but this isn't my first rodeo, and I had no problems with my previous 914 (a 1.7). For this car, I set the valve clearances to .006" intake and .008" exhaust, which is spec for a 2.0 (from what I found).

While I was under the car, I also confirmed that I have stock aluminum pushrods.

Compression and leak down are valid next step and will turn up issues if valves aren’t adjusted properly. Leak down would be preferred so you can narrow down the source of leakage. Leak down is another infrequently used specialty tool that not everyone has and takes a little practice to use properly so understand if that’s not an option.

I have a compression tester at home, but I don't think it does leakdown. I'll check when I get home and order a leakdown tester if I need one. Any excuse for more tools! (IMG:style_emoticons/default/cheer.gif)

One thing I forgot to mention earlier, is that whenever I disconnected a vacuum hose for testing, the idle would jump up until I either plugged the port or connected the gauge. So, that also seems to rule out a vacuum leak.

I also made sure the AAR was closed before I did any testing.

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Edit:
I wonder if I might have a valve seat coming loose. Leaking around the valve seat might explain why I can get an okay idle speed while sitting in the driveway, but it jumps way up once I drive it, which has happened to me both times this scenario occurred. Yeah, I'm reaching, but running out of ideas....

[Superhawk996]

Edit:
I wonder if I might have a valve seat coming loose. Leaking around the valve seat might explain why I can get an okay idle speed while sitting in the driveway, but it jumps way up once I drive it, which has happened to me both times this scenario occurred. Yeah, I'm reaching, but running out of ideas....

There are still plenty of other things it could be . . . Not many good . . . But do the compression / leak down / MPS vacuum test before we start thinking about the uglier possibilities