Thanks for the suggestion, but as mentioned in at least one previous post, I have tried 2 different MPSs. One of them was good except for a blown diaphragm (which has since been fixed) and the other was re-calibrated to factory specs and is in the car now.

I believe I've done a pretty complete job of documenting all of the things I've tried already- including 'the basics'. It's a lot of reading to go through the whole thread, but I appreciate anyone who is willing to do so to help.
I welcome the input, so if there's something I've missed keep the ideas coming.

Robert I have a new-ish FI wiring harness and 043 ECU I can loan you for testing. Which ECU do you need?

So once at band camp..........


Electrical connector primary circuit somewhere....maybe even at the.fuel pump... loose or high resistance. When it gets hot....poof.

Could be the connector at the ecu is not seated completely.

My
02

I have a spare ECU that I will swap in tomorrow. If that doesn’t take care of it I’ll likely take you up on your offer to borrow (or rent) your FI harness for testing.

Thank you!

Godspeed Robert. This is definitely one we need to learn the final results on. You have chased it hard and carefully to seemingly the ends. Can't wait to learn what gremlin it is. Best of luck!

When you stall, is your coil nuclear hot? Like so hot you can't keep your hand on it? If so...that could be your problem. I had that issue on my yellow car and solved it wiht a ballast resistor. Never stalled again and the coil never got hot. I know, we shouldn't need one, but...

Thanks- I never checked the coil to see if it was, but I did try swapping the new Bosch blue coil I installed when I bought the 123 distributor out with stock coil when it wouldn’t stay running and it didn’t solve the issue. The new coil is back in.

Update to the ongoing saga..apologies in advance for the long post.

Installed a brand new ignition harness (a work of art by Jeff B) but the stalling issue remains, although it took a bit of a different shape yesterday.

After installing the ignition harness, I drove the car without any issues for ~30 minutes trying to get the AFR dialed in on the MPS. Drive, pull over, adjust, repeat. Idle always steady at 1k. When I pull over to make another adjustment, before touching anything the idle starts dipping to almost stalling the car and back up to 1k over and over as if the MPS diaphragm had just cracked. After about a minute of this as I'm wiggling wires, checking hoses, etc. While it's doing this the AFR is super lean (~16+), yet the only way I can keep it running for the drive home is to open up the throttle body screw to let more air in and stay on the go pedal. I'm only 4 miles from home, but the AFR is so high that I worry about cooking the engine so I pull over after 2 miles to let the car cool off a bit. I get impatient and after several minutes start it up again and within a few minutes of limping home the problem goes away and the car is back to normal, but when I get back in my driveway the problem returns and I can't keep the car running. I check the MPS and it's holding vacuum just fine.
Something that I noticed as it was surging was air coming out of the hole in the passenger side tin that is to the left of the distributor. At first I though a hose had come disconnected. Can't remember if I feel that air blowing when the car is running normally and since it's not running at the moment, I can't check. Maybe this is just the from the impeller?
So do I try replacing the injection harness now?

And a side question about MPS adjustment and cold idle:
I was able to get the AFR to ~ 13.4 for par load and 13 for WOT. Maybe not ideal, but the car seems to like the AFR on the rich side. However, the AFR at idle is only ~12.5-12.9. If I try to raise it by adjusting the MPS, the part load AFR is then too high. If I try adjusting it using the throttle body screw and ECU knob, the idle is too high.
In other posts I see where people have an AFR above 14 at idle.

Lastly, I have a working AAR valve, but when the car is cold the idle speed only goes up to ~1100 rpms or so. If I plug the hose the car dies, so I guess it's doing it's thing, but my understanding is that I should be seeing much higher RPMs when cold, no?

Bump out of desperation.

Should I feel a fair amount air coming up from the engine through the tin on the passenger side? Leak at the head?

Can you be more specific about where air is coming from? Doesn’t seem right.

Sort of grasping but have you done a compression check?

It's ok, I'm grasping too. I haven't done a compression check but planning on borrowing the tool to do so tomorrow.

Air is coming from the hole in the tin just above where #4 is stamped in the tin, and also through where the CHT wire comes out of. I’m told head leaks are loud, but no abnormal sounds though.
Click to view attachment

Did you ever rule out the ecu?

I did

If all of your components check out, replaced your FI harness and you are still having problems i would suspect the power feed to the fuel pump and the ground. It would be the only thing that you have not replaced. When cold it works and when it runs and gets hot looses connection until it cools down again.
Also when building my car i bought new relays from 914 rubber and some of them did not work when i plugged them in so i had to spread the out the legs and then was all good. Maybe you are having a loss of connection a like that?

Thanks- Verified fuel pump is running and fuel pressure is at spec when it stalls,

I’m still hoping someone can tell me why I am feeling air come out the passenger side engine tin when the car is running. I’m worried there is an issue with the head seal but from what I’ve read it would be really noisy if that was the case. No?

On my car the hole in the tin above the #4 holds a small plastic spark plug wire guide. Also, there should be a rubber seal in the hole where the CHT wire comes through the tin. For optimum cooling you should "seal" all holes in the tin with the factory component that is meant to go there or something else. For example, missing spark plug wire seals let out gobs of cooling air.

Regarding your intermittent stalling, I read this whole thread one time and I recall that you mentioned that you checked your grounds but I don't recall you saying which ones you checked. Did you check the tri-prong FI ground on the top of the engine, the ground under the relay board behind the driver and the transmission-to-body ground on the trunk floor? My apologies if have repeated something.

if he replaced his fuel injection harness the grounds on top of the engine would go with the harness
i believe a bad trans to body ground would make it hard to crank the engine when warm.
Has to be in the harness to the brain because he says everything else is new and checks good when it wont start.
The air that you are feeling blowing when the engine is running is from the cooling fan. Unless i misunderstood you.

I replaced the ignition harness but not the injection harness.

Compression #s with engine warm, all plugs removed and throttle open:
110, 110, 130, 131

Just wanted to dust the cobwebs off of this thread with an update. I installed a new Bowlsby injection harness (work of art!), and so far...so good. I'm probably jinxing things just by posting this. I hate intermittent issues, and given how intermittent this issue was, I won't be confident that the car won't stall on me again for some time.

Two questions remain:

1) If I leave the air temp sensor plugged in (sensor on the plenum), when cold the car runs fine, but when it warms up, the idle hunts like crazy. If I unplug it the idle is steady both when cold and when it's warmed up.

2) I can't get the idle lower than 1100 rpms. This seems to be an issue others have after installing the 123 distributor and happens whether I configure the distributor it for retard or advance. I don't have a vacuum leak, but I did notice something on both my original throttle body and the NOS one I found last year: When the idle screw is all the way in, a fair amount of air is still being pulled from the top of the butterfly. If the adjuster is all the way in, shouldn't it completely (or nearly completely) block any air from getting in?
Click to view attachment (borrowed pic)

So I'll give you two and one as a partial victory, pending additional info. Hopefully the wiring harness was the ticket. It would make sense. Intermittent issues could easily be caused by a sketchy wiring harness. Fingers crossed.

In terms of your questions: 1) you are lean at idle. Unplugging the air temp sensor is going to somewhat richen your mixture, and the hunting idle was because it was lean.

2) I think that's normal. I'll go see if I can find one of my TB's and compare, but there are several versions of them, so I may not be able to answer that definitively. Yes, with my 2056, D-Jet, 123 Dizzy, using curve "B" I couldn't get the idle below 1100. I kind of got used to it.

Rock on

@BeatNavy I'll take as many as I can get. Thanks and I appreciate all of your help along the way on this one.

So maybe I should go back and re-calibrate the MPS with the air temp sensor plugged in (and engine warmed up). The perfectionist in me hates knowing it's unplugged.


RE throttle body: I found a pick of a bunch of different stock versions, including ones that didn't have the hole drilled through the butterfly plate. If I cover up that hole the engine dies (which supports my belief that I don't have a vacuum leak). However, if I cover up just a bit of the port that's associated with the idle adjustment screw, I can easily get the idle below 1000 RPMs.
I also found a thread that a rebuilder of TBs had posted here a while back saying that part of his service was to ensure that the idle bleed screw fully sealed the port when screwed in all the way. It would make sense to me that it should function that way.

Thanks rj for helping me to think about my 1974 2.0 liter running problem last year (it was the timing all along!)

Anyway, my 1974 1.8 had an intermittent problem with dropping out and stalling and it was the ignition switch. Maybe a long shot, but I didn't see you mention it. I could stop the stalling by manually holding the switch ever slightly like I was going to start the car.

I was going to try to be clever and say maybe it's your driveway since it seems to stall there a lot...

Good luck!

Paul

Ok I'm back to updating my thread that seemingly never ends. I thought I had my problem of high and/or surging idle and/or intermittent stalling issue fixed with the new ignition and new injector harnesses.

Nope.

Car hasn't stalled again, but almost did. Started the car the other day and after it warmed up the idle was a perfect and steady 1000rpm. Which was strange since I couldn't get it below 1200rpm previously. AFR was 13.5 too, even though the last time I had driven it it was 10.5 at idle.

Drove ~ 15 minutes to the grocery store. All good. When I got back to the car the idle was now at 1100rpm. Another 15 minutes of driving and idle increased to 1200rpm.
More time driving and the idle started fluctuating from 600-1200rpm. At one point at a stop sign the engine almost stalled- idle just dropped to almost 0 like the engine had just been turned off, but the idle came back up before that could happen.

I did notice that when the idle is fluctuating (usually going from ~600-1200 rpm) it will continue to fluctuate even if I step on the gas a bit and hold it there- say increase the RPMs to 1500rpm, the rpms will continue to drop to about 1200 and then go back to 1500. So this issue is happening even when the ECU is not seeing an 'idle' state because the TPS is seeing idle anymore.

The nagging feeling that maybe there is a vacuum leak wouldn't go away so I connected my vacuum gauge via a T off of the throttle body retard port and it shows 17.inHg at 1100rpm and when it surges to 1200rpm it reads 18.5in.Hg. Of course when I did this test the idle wasn't dropping below 1100rpm so I don't know what the reading would be then, will try and capture that. My guess is that it will be less than 17in.Hg just by virtue of the slower engine speed. In other words- I don't think i have a vacuum leak because I would expect the vacuum to drop at higher idle RPMs if that was the case.

This feels like an issue with the FI system or the engine itself. But I've got a new ignition harness, new FI harness, new CHT, 123 distributor, injectors tested, verified fuel pressure, etc. I've tried swapping ECUs and I've got a rebuilt MPS that holds vacuum. I suppose I could try putting the vacuum gauge between the manifold and and the MPS and see if the MPS diaphragm is intermittently failing? Could this be a thing?

What about the engine itself? What are the symptoms of leak at the heads? Compression issue? (Current #s are 110, 110, 130, 131) Other? Car seems to have plenty of power.

Obviously you did the compression test with warm engine ? you do have a high percentage variance in compression ,did you reset the valves before the test?.
Good luck.

Yes, engine was warm when I checked the compression and valves adjusted.

A local member had the same 'hunting' (fluctuation) problem. The stacked elbow looked good but was broken in a spot you couldn't see. Have you verified the internal plenum tubes are not cracked? The bottom side as well as the top.

I know this theory may be completely invalid, but where is your PCV plugged into? Is it the stock location? Just wondering if an aging valve can cause inconsistencies in idle performance. I moved mine above the TB. Things seems to steady out but I made a bunch of other adjustments and changes, so hard to say.

'75- no stacked elbow and no PCV.

And a vacuum leak wouldn't account for the engine almost cutting out- the RPMs would go up, plus I measured no loss of vacuum when I put the vacuum gauge on the TB, even when the idle was fluctuating.

Did you ever replace the board on your TPS? 914 rubber sells them

No, and not discounting it, but I'm stuck on how it would explain the engine stalling since the car will still run with the TPS unplugged. I did clean the board last summer even though the contacts looked good. It's been calibrated.

Something about the idle changing with amount of running time keeps pointing to a vacuum leak. Isn't it possible that the throttle body has a leak underneath it where it attaches to the plenum? The rising temperatures open it and then it closes again after cooling. Just had to throw my 2 cents in. Sure sounds like a vacuum leak. All the best....
gg

I'm open to anything being possible at this point. However, I when I had a vacuum gauge hooked up to the TB below the butterfly while the car was idling, the gauge showed 17inHg with no loss of vacuum when the idle fluctuated up- in fact the vacuum increases when the idle RPM increases. My understanding is that vacuum at idle below the TB should be anywhere from 15-18inHG, so I'm on the upper end of that.
A vacuum leak also wouldn't explain the engine wanting to stall.

Appreciate everyone's ideas. Keep 'em coming.

Another WAG, but if your TPS is worn and intermittently telling the ECU you're at idle, I can see how you can go way rich or lean sporadically (depending on ecu and MPS settings) especially as engine compartment temps change.

Do you have a variable resistor between the cht and ecu? I find that adds an extra knob to dial everything in.

I like WAGs.
The premise makes sense to a point, but then doesn't explain why when the idle surge is happening, the rpms continue to surge when I open the throttle a bit and hold it in that position. In that condition the TPS wouldn't be reporting an idle state to the ECU.

I don't have a resistor between the CHT and ECU. Car ran great for 7+ years without one before this issue cropped up, so I haven't felt a need to put one in. I've also got 3 CHTs that I've tried, both used and new ones. All test in spec when measuring resistance cold and warm.

Have you taken the tri-ground and actually taken out the case bolt and cleaned it to make sure it isnt loosing ground while warm? It seems like you have done virtually everything else. It sure seem electrical somewhere.

It seems like 2 different things happening here.
The surging from what i understand tends to be a lean issue typically caused by a vacuum leak and the stalling would tend to be a heat related electrical issue.
How do the spark plugs look? Are they all colored tan or is one or more white?

Do not assume anything is good until you 100% rule it out. Go to 914 rubber and buy all of the vacuum elbows, connectors, TB gasket, cold start injector gasket ect.. Auto Atlanta has a good vacuum line kit too, Put clamps or good zip ties on the plenum to intake runner hoses and also it is not unheard of to have a crack in the plenum itself.
Check the intake nuts for proper torque too.

For the electrical issue make sure as stated above, remove and clean the 3 prong ground for the FI and then go to every other ground one by one and do the same.

Hope you find it soon. Unfortunately this is how most of us learn about these cars.

All vacuum hoses are new and have zip ties on them. Intake hoses are new. Gaskets for the intake runner, TB and cold start injector are new. I tore down all of the FI and intake stuff and cleaned it and checked the plenum for leaks

Used a smoke machine to hunt for any vacuum leaks. Used vacuum gauge at idle to verify vacuum was in speck (17inHG).

Bolt that grounds the 3prong connector on the FI harness was removed and cleaned up (it already looked fine but looks better now).

Vacuum doesn't seem to be the issue- at least not on the topside of the engine.

Haven't checked the ground point under the relay board. What wire is connected to it?

Robert, sorry this issue has resurfaced It's either so obvious it's staring us in the face or buried so deeply we can't find it among the usual suspects.

Those are good suggestions about the relay board. Is that in good shape? It's a little tedious, but since you've tried just about everything else, you may want to remove the relay board from the car and test continuity between the traces. As a minimum once you remove the relay board you'll see the multi-wire ground in front and below the board that it's connected to. Worth cleaning, inspecting, tightening, etc.

Not long after I picked up my '72 I went through the whole D-Jet. The relay board was suspect, so I removed that for some TLC. While I was at work my wife actually took the time to scrape all the tar off the back with a bucket of solvent so I could inspect and repair. Nasty job, bless her heart (come to think of it, that may have been the LAST thing she did for me on that car.... ). Anyway, I did end up finding some questionable connections and soldering or reinforcing those before sealing it back up again.

EDIT: Sorry, Robert, I realized initially I put a "happy face" in the first sentence. Not my intention. It's changed now in my post (anyway) to a sad face to show that I know this sucks. I'm sure that makes you feel a LOT better....

Good suggestion- you probably can guess how I'm going to answer- I have a stack of 4 relay boards and spare relays. Continuity has tested good on all of them, although I swapped the one in the car out anyway. I will check the ground connection there though, somehow I missed doing that.

Just a WAG , check the ground strap from the transmission to the body

Done, but keep 'em coming.

Not sure it is possible to cause a stall but is your ignition switch goofy?

It's crossed my mind, but because the stalling seems to be tied to the idle fluctuation, I'm inclined to think the ignition switch is ok.

So when the car is warm it idles down and stalls? Not like it cuts off.
Is the decel valve functioning? On my 73 with everything nos or rebuilt it has some strange return to idle behaviors and I just assume that it is the goofy old d-jet. When warm the engine returns to idle pretty slowly and sometimes stays around 1,200 rpm for a bit before settling down but often times the light will change and you are off again before it completely idles down.
With how off your compression numbers are you only have that remaining
A friend reminded me of the product Sea Foam the other day and he runs a can through his fuel tank every once in a while to keep everything super clean

Everything is intermittent. When it does stall it stalls immediately when taking my foot off the gas pedal with seemingly no loss of power beforehand. Usually by the time I limp it home, the stalling goes away. :/
To be fair, the car hasn't stalled since I replaced the ignition and FI harnesses, but I haven't driven it that much either.

The idle surges are intermittent too. The last time I took it out, the idle was stready at 1000 RPMs after warmup. After driving it a bit, the idle crept up to 1200, but was steady. More driving led to the idle surging from 600-1200rpm. Got back home and the idle surge range changed to 1000-1200rpm.

Seems like if it was a compression issue it would be constant and the engine would be lacking power, which doesn't seem to be an issue. But maybe that's not always the case?

Robert, I haven't read the entire thread, so pardon me if this has already been addressed.

Which cylinders have the low compression #s. 1. ____ 2. ____ 3. ____ 4. ____

Have you performed a valve adjustment? If not, do so, then check compression again.

I had a hunting idle on the '71 (1.7L) when I first acquired the car. I replaced all the vacuum lines, adjusted points, set ignition timing, etc., but after adjusting the valves (right bank valves were too tight, not completely seating), the hunting stopped

No points lost for not reading through the whole thread. It's a lot to go through. I thought about starting a new post that starts off with everything I've tried, but then I'd have to re-read it myself.

Valves have been adjusted.
Compression check on warm engine: cyls 1 & 2: 110, cyls 3 & 4: 131

I'm on pins and needles! What is the latest on your intense diagnosis? I'm dealing with something similar and have read all of this thru a search and I'm listening to all of it.