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.

[Sea Rooster]

Following....I have the same issue.

[JeffBowlsby]

Im no guru, but the air screw is doing what its supposed to. 1/4 turn on it (90 degrees?) is actually quite a bit and sounds excessive.

1. Try turning the air screw much less, say 20 degrees at time to reduce the idle rpm, but not shut the engine down.

2. Idle mixture is set by the ECU knob which adjusts the ECU. For that knob to function, two contacts in the TPS need to be in contact to signal the ECU to take control of idle functions. All to say, confirm that your TPS is functional for all 4 circuits and that the TPS is calibrated correctly which will signal the ECU to control idle.

3. Check for other free air leakage locations, this can get tough - be thorough until you find a leak if it exists. AAR closed when warm? Injector gaskets well seated and not causing an air leak? Use a smoke pencil on the intake plumbing to check for free air making its way around gaskets, the TB pivot bushings, the air plenum etc.

Hopefully this solves it.

[BillC]

Im no guru, but the air screw is doing what its supposed to. 1/4 turn on it (90 degrees?) is actually quite a bit and sounds excessive.

1. Try turning the air screw much less, say 20 degrees at time to reduce the idle rpm, but not shut the engine down.

2. Idle mixture is set by the ECU knob which adjusts the ECU. For that knob to function, two contacts in the TPS need to be in contact to signal the ECU to take control of idle functions. All to say, confirm that your TPS is functional for all 4 circuits and that the TPS is calibrated correctly which will signal the ECU to control idle.

3. Check for other free air leakage locations, this can get tough - be thorough until you find a leak if it exists. AAR closed when warm? Injector gaskets well seated and not causing an air leak? Use a smoke pencil on the intake plumbing to check for free air making its way around gaskets, the TB pivot bushings, the air plenum etc.

Hopefully this solves it.

I've already done the leak checking with a smoke machine (mentioned in the un-DAPO thread). So, it's confirmed there are no undesired leaks in the intake system. Also made sure the AAR closes properly when warm.

I've been trying to adjust the idle air screw in small increments. Unfortunately, I can make multiple small adjustments (5-10 degrees) with no change in the idle, and then one more little tweak will cause the engine to start it's downward spiral. Once that starts, I need to back the idle screw out like 1/2 turn or more to get it back to 1600 RPM.

It's quite possible the TPS is not adjusted properly. It's one of the few things I haven't adjusted from the previous owner. My plan, when I replace the TPS board, is to just remove the whole throttle body from the car and adjust it on the bench before reinstalling.

Anyone got a link to the TPS adjustment procedure?

[Ron914]

Im no guru, but the air screw is doing what its supposed to. 1/4 turn on it (90 degrees?) is actually quite a bit and sounds excessive.

1. Try turning the air screw much less, say 20 degrees at time to reduce the idle rpm, but not shut the engine down.

2. Idle mixture is set by the ECU knob which adjusts the ECU. For that knob to function, two contacts in the TPS need to be in contact to signal the ECU to take control of idle functions. All to say, confirm that your TPS is functional for all 4 circuits and that the TPS is calibrated correctly which will signal the ECU to control idle.

3. Check for other free air leakage locations, this can get tough - be thorough until you find a leak if it exists. AAR closed when warm? Injector gaskets well seated and not causing an air leak? Use a smoke pencil on the intake plumbing to check for free air making its way around gaskets, the TB pivot bushings, the air plenum etc.

Hopefully this solves it.

I've already done the leak checking with a smoke machine (mentioned in the un-DAPO thread). So, it's confirmed there are no undesired leaks in the intake system. Also made sure the AAR closes properly when warm.

I've been trying to adjust the idle air screw in small increments. Unfortunately, I can make multiple small adjustments (5-10 degrees) with no change in the idle, and then one more little tweak will cause the engine to start it's downward spiral. Once that starts, I need to back the idle screw out like 1/2 turn or more to get it back to 1600 RPM.

It's quite possible the TPS is not adjusted properly. It's one of the few things I haven't adjusted from the previous owner. My plan, when I replace the TPS board, is to just remove the whole throttle body from the car and adjust it on the bench before reinstalling.

Anyone got a link to the TPS adjustment procedure?

Hi Bill ,
It's on the 914 Rubber TPS purchase page. Its in the installation section for the TPS

[Superhawk996]

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.

Incorrect

The 012 CHT forces an overly rich condition until the engine is hot which is totally consistent with you having to give it enough air to keep running. Then once it’s hot (200F) it’s forcing a lean condition if you don’t have the 270 ohm ballast resistor in place.

Get the correct CHT and ballast resistor in it then reevaluate

All data below is the CHT sensor only (no ballast resistance included)

[emerygt350]

That's what I was thinking too. Although it seems to be too rich at hot as well, not going lean. Verify the mps and ECU are correct for 73 and matching while you are in there. Until those are known, the TPS is set correctly, and you get the right cht and ballast resistor, I wouldn't mess with anything else.

[Superhawk996]

That's what I was thinking too. Although it seems to be too rich at hot as well, not going lean.

Good point but:

1) I guess I’m not sure what his actual operating temp is and how much “leanness” as a percentage of what he’d actually be getting without the 270 ohm ballast resistor in place.

2) I ASSUME ( (IMG:style_emoticons/default/chair.gif) ) there is also some interplay in the 73 MPS & 73’ 1.7L/2.0L common ECU that also enriches the mixture via the unique 037 MPS in order to be used with the 2.0L. Said a little differently, I don’t think it was only the 73’ unique CHT + ballast resistor combo that was responsible for “extra” enrichment for the 2.0L. Anders and/or Dr. D-jet cover this somewhere on their sites. I have not personally deep dived the details here so I could be wrong.

I also think that if the TPS isn’t indicating idle state at closed throttle, that could be adding to the “richness” uncertainty.

I just know the 73’ is a bit unique and I’ve only had success with a matched 73’ system. Someday I really need to think about getting all the 74’ stuff to escape the 73’ parts that are getting rare. Or more likely, just go Megasquirt.

[Superhawk996]

I guess I am also assuming the vehicle has a 73’ ECU.

[emerygt350]

Yeah, we need verification it's all 037. The only difference besides tuning I know of in the 73 mps is that spacer. Which is a big change from the 1.7 of course.

[BillC]

So, I installed the 017 CHT and 270 ohm ballast resistor. I also replaced the circuit board in the TPS and adjusted it according to the video on 914Rubber. Unfortunately, drivability is worse (now has a big part-throttle stumble), and I still can't get it to idle down where it should.

However, I may have found the issue(s):
-- First, the ECU is part # 0 280 000 037, which Brad Anders' page says is for a '72-'73 1.7 (it doesn't have the the CU13X marking for a '73 2.0).
-- Second, the MPS is 0 280 100 043 (039 906 051), which Brad's page says is for a '74-'76 2.0. It is also labeled "Remanufactured by Fuel Injection Corp".

This is what I get for not double-checking everything from the DAPO(s). (IMG:style_emoticons/default/headbang.gif)

So, at a minimum, I need to make the parts match.

If I get a '74-'76 2.0 ECU (0 280 000 043 or 044), that should work with my MPS and the previous CHT, right?

[emerygt350]

Yes, and that is exactly what I would do.

And also, getting that TPS right is a bit of an art so it may take a couple attempts. Don't bother with it till you get matching parts though.

[Robarabian]

Test your MPS.. this sounds MPS related to me... assuming no leaks, no throttle body leak and everything else working.... my vote is the MPS..

[Olympic 914]

Part of your problem may be that the tuning on the 043 MPS is leaner than that on the 037 MPS.

you can see the figures on Anders site

However the 043 MPS CAN be adjusted to the same spec as an 037 MPS and beyond.

Also, since your 043 MPS has been rebuilt, you really don't know what its settings are.

If you have access to a vacuum pump and a Wavtec meter you can check and adjust your MPS.

There are many that profess that all the FI parts MUST match.

I somewhat disagree.

I have 25,000 miles on my rebuilt engine and it runs great. but it will not idle on a cold start. (I just deal with it) after about 1 mile it will idle fine.

My setup on a 2056 is the same ECU you are running, a 037 (its the original from when the car was a 1.7) CHT is the 012 and I do not have the 270 Ohm ballast resistor installed. also the MPS is a 043 unit that I have adjusted to richer than the 037 specs (again 2056)

I don't have those numbers in front of me now.

Now I have done a bit of tuning on the MPS using a wideband AFR that is installed under my dash and I regularly monitor.

Both the 017 and 012 CHTs read about the same when hot < 90 ohms, all the ballast resistor on the 2.0L does is trick the 037 ECU into richening the mixture.

So, I installed the 017 CHT and 270 ohm ballast resistor. I also replaced the circuit board in the TPS and adjusted it according to the video on 914Rubber. Unfortunately, drivability is worse (now has a big part-throttle stumble), and I still can't get it to idle down where it should.

However, I may have found the issue(s):
-- First, the ECU is part # 0 280 000 037, which Brad Anders' page says is for a '72-'73 1.7 (it doesn't have the the CU13X marking for a '73 2.0).
-- Second, the MPS is 0 280 100 043 (039 906 051), which Brad's page says is for a '74-'76 2.0. It is also labeled "Remanufactured by Fuel Injection Corp".

This is what I get for not double-checking everything from the DAPO(s). (IMG:style_emoticons/default/headbang.gif)

So, at a minimum, I need to make the parts match.

If I get a '74-'76 2.0 ECU (0 280 000 043 or 044), that should work with my MPS and the previous CHT, right?

[BillC]

And ... it appears to be solved! (IMG:style_emoticons/default/piratenanner.gif) (IMG:style_emoticons/default/cheer.gif) (IMG:style_emoticons/default/aktion035.gif)

I dug around in my parts stash last night and found an 037 MPS in the box. No idea how long ago I bought this, because I completely forgot I had it.

Anyway, I replaced the old MPS with this one, reset the knob on the ECU to match the tiny melt mark, and the car started right up! Once the car warmed up, I adjusted the idle bleed screw, and now it idles very well at 900-1000 RPM. Won't have a chance to actually drive it until later today, but I'm feeling optimistic. (IMG:style_emoticons/default/driving.gif)

[JeffBowlsby]

Shazzam! Amazing what the right parts will do. Congrats.

[emerygt350]

That is great. And inexpensive!

[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.

[BillC]

Thinking about it, do I have the distributor set correctly? IIRC, it's on curve "A".

The 123Ignition manual shows that is the correct curve for a '73 2.0. However, the manual also has a note of "DEGREES NEGATIVE VACUUM !!!" What does this mean?

I have the vacuum hose from the throttle body attached to the front port, which should be the vacuum advance position. However, that note in the manual has me wondering if the vacuum line should be hooked up to the rear port for vacuum retard?

[emerygt350]

Absolutely change that to the rear facing port.