Drove around for 30 minutes in 80+ degree weather. All arterial roads, so several stop lights, etc. No problems until I was almost home. Car stalled when I stopped at a light. RPMs just dropped to zero. Was able to start it again with a little difficulty and had to keep my foot on the gas to keep it from stalling out again. Power seemed ok though the rest of the way home (I think). It stalled once again at a stop light a couple of blocks from home and then again when I pulled in the driveway. I let it sit for 30 seconds, started it again and it idled just fine. Rock solid at 1000 RPMs. Pulled it into the garage where it sits now.

Prior to today the car has been running and idling perfectly since I went through the FI parts last year, which included installing a 123 distributor, new CHT sensor, a newly rebuilt mps (calibrated for correct afr on my engine), new vacuum hoses, NOS throttle body, rebuilt injectors, new fuel pump, valve adjustment and timing.

I haven’t checked the AFR since last year, not sure why it would change though.
It’s a ‘75 so the fuel pump is in the front, so I can rule out vapor lock I think.

Anyone have ideas as to why it would be stalling?

What was your AFR last year?

Last setting I made note of: 13.5 at partial load, and 12.5 at WOT. Idle at 12.2.

Will check it again this week.

Hey Robert,

12.2 seems pretty rich at idle, IMO. I'd shoot for 13 or 14+, although take idle AFR's with a grain of salt -- the volume and speed of the exhaust gasses have much more error built into them at idle than other loads. I'm dealing with that now (apparently).

The symptoms you describe sounds like it's going too rich at idle when warm, although I'm not sure I'd correlate your AFR with that or not. I'd start looking for other symptoms along that line.

Just to confirm: no problem at load, just at idle?

Correct- just at idle, and just the one outing. Idle speed (except for when I couldn’t keep it running) is a solid 1000 rpms.
Hope to look at the afr numbers again tonight.

Maybe lean out your ECU knob a few clicks (it has very small impact) and see how that does. If idle becomes unstable, probably have gone too far.

Or there is something else going on...

Presuming it's a 1.8L (75), try the dual relay (under the battery tray) - exactly describes what happened to my 74 1.8L about a year ago. Chased it for 6 months. When in/down there, check the capacitor, too; I had a loose wire that may have contributed to the situation.

It's a 2.0 liter. Sorry, should've clarified.

If I change the ECU settings the idle starts to hunt. Really it's been running perfect and for fairly long drives without any issues. No issues detected right before it died when stopping at the light, and then again a few blocks later. Power was fine for the entire 30-45 minute drive, right up until it died. Then power seemed ok I think, but may have been low. Seems odd that it would stall twice in the space of a few minutes, then after sitting 30 seconds fire right up and hold idle just fine (like it did before it stalled).

I haven't taken it out yet, but am a bit afraid to try to take it out to get AFR readings and adjust the MPS for fear that it' will leave me stranded.

Someone suggested looking at the coil. I replaced that last year with a new one. Doesn't mean it couldn't be bad, but how do you test an intermittent coil issue?

So I went to see if I could drive it around and measure the AFR and when I started it up cold, the idle stayed at 1000 RPMs for about 10 seconds (which is lower than where the idle should be when cold) and then stalled. After starting it again (it starts quickly) it only lasted a few seconds before stalling. I did have enough time to verify that the AAR is working correctly before pushing it back into the garage.

Hoping it's the coil since i have a known good spare. Will try swapping coils this weekend unless someone has another idea for me to try.

if it is a 1.8 the air flow meter flap could be sticking and that would cause your problem. They get hot and the device expands causing the warped flap to stick in the bore, and suddenly the control unit thinks that the car is running at 140 miles and hour and adds all of the extra fuel. As long as you have your foot in it, it is just running rich, but as soon as the car comes down to idle it cannot handle the extra fuel and floods out. THEN the air flow meter cools a bit the flap unsticks, the car starts, and it as if nothing has happened. Check the oil level as well, as this condition causes the extra richness to dilute the oil with gas

2.0 Djet. I think a 123 distr.

My quess is a kinked fuel line underneath the rack cover.

Check your fuel pressure.

Second best quess is there is vacumm leak. Sure you have the ported vacuum line to the 123 set up right?

Yes- Djet 2.0, 123 distributor.

Doubt a fuel linked itself after several months of not being kinked.
Vacuum leak would cause high idle.

I’m starting to wonder if my new (to me) MPS went bad with a torn diaphragm.... will check to see if it holds vacuum and report back.

MPS yes...that is a symtom of a cracked diaphram..BTDT.

I quess where I was going with the 123 dizzy comment is are you running ported vacuum to the dizzy?

No vacuum lines to the dizzy.

Ok, tried adjusting the MPS, but can’t keep the car running after it warms up unless I’m on the gas. Revs easily though.

Pulled vacuum on the MPS and it does leak. About 1 inch per 2 minutes. So that’s no good.
To make sure that’s the issue, if I disconnect the vac hose from the MPS the car will also stall.
Should it idle with the hose to the MPS disconnected? (Albeit maybe badly)
Actually, I just realized that if the hose was disconnected from the MPS it would think the car was WOT and flood it with gas which would cause it to stall, right?

I guess I’m rebuilding the MPS to see if that fixes the issue.

Yes. Do you have access to a spare MPS for testing? I've got a spare 043 I could loan if you need it. May take me a day or two to send. The alternative is to go ahead and drill this one out and verify a bad diaphragm and get the repair kit from Chris.

That’s a very generous offer, thank you.
The MPS I have was already opened up and I have a spare rebuild kit for it. I bought it as a recalibrated unit from Jeff Bowlsby last year, but it still had the original diaphragm I think. If I can’t get it to seal after rebuilding it I may take you up on your offer.

Went to rebuild the MPS.
I opened it up and the diaphragm was fine. Cleaned everything off put it back together and it still didn’t hold vacuum as well as it should. I actually have another MPS that I tried to remove the outer screw on awhile back and totally buggered it up. So just for fun I took the bottom part (where the vac line connects to) of the MPS I was running in the car and replaced it with the bottom of the other MPS I had and cleaned all the seals gasket etc. and put it back together to see if it would hold back in better.
Vacuum held better, a little bit of a leak down but less than 1 inch after five minutes. Installed it an the car stayed running. Got the idle dialed in. Great, fixed!
Went in the house for lunch and came back out an hour later to drive it.
Car wouldn’t stay running again,
Tried swapping the coil with a known good coil- no change.

Then I realized I didn’t hear the fuel pump running. Discovered my relay board was bad. Man, all this work and it’s the fuel pump. How did I miss hearing that it wasn’t running?! Swapped out the bad board for a good one and the pump starts running again and everything was great car idles perfectly. Took it out for a spin and as soon as I drive 1 block and let off the gas the car stalled again. I verified that the pump is running so the bad relay board must’ve just been a fluke in the middle of things.

I’m at a complete loss now. MPS is leaking but just barely. Is it still a suspect?

No, leaking an inch every 5 minutes is well within spec, IIRC. Something else is going on. What a mess, eh? It's hard enough troubleshooting one thing much less 2 or more things. Back to fundamental troubleshooting

Small leak or worn TB bushings yes, but not if it's a large leak. A large leak would act like the OP's issue.

Are the vacuum hose to plenum in the correct spot? Not the same but when I had my 2.0 with SDS EFI (stock djet intake) I connected the vacuum line into the wrong port and it wouldn't idle worth a crap. I swapped the hose to IIRC the correct djet MPS port and it solved the issue.

I was going to ask if you listened for the fuel pump running. Mine was doing the same thing and it was a faulty fuel pump intermittently stopping. If the MPS was the culprit it usually means constant rather than intermittent behavior.

Car has a NOS throttle body. Hoses are in the right spot. Car was running perfectly for ~9 months. Hadn’t touched anything until it started stalling. I thought I had it fixed twice-once when swapping the MPS parts and again when the fuel pump wasn’t running. After each ‘fix’ the car idled for several minutes without any issues.

Car seems to have plenty of power when I’m on the gas. Instantly dies if I let the RPMs drop below 1600 or so.

Well...I’m perplexed.

Started it up and cold, the idle was too low. Decided to start at zero again and took another run at getting the MPS, the TB idle adjustment screw and the ECU knob set correctly. I had started moving the settings of all of these all over the place when trying to get the car running before.

Car is purring again and I was able to drive it a few miles without it stalling. Ran great with plenty of power.
AFR 13.1 at idle. Best I could get. Need to dial in the AFR at WOT still but it’s in the ballpark.
In the end, the only thing I really did was clean and reseal the MPS. I don’t trust it for a long drive yet. Time will tell. I have a hunch that the fuel pump may have an intermittent issue since the supposedly bad relay board I took out when the fuel pump wouldn’t run ended up testing good for continuity.

It’s back. Was running fine with no issues for several long outings. Then yesterday it started happening again after 20 minutes of driving. Verified the fuel pump is working.
Power seems fine above 2000rpm. If I press in the clutch and let off the gas the RPMs drop to zero and car dies.
When it’s in this state, in neutral the car does not rev smoothly when below 2000rpms and is hard to keep running. If in gear and driving, I can keep the car running without any real issue as long as I’m giving it gas.

Each time after it dies it starts right up no problems, but I do have to keep the rpms up to keep it running.
Something else I noticed was the rpms kind of jumping erratically up 100 rpms while maintaining a constant speed on the freeway. Hadn’t seen that before.

Given everything I’ve already tried to solve this, I’m starting to suspect the 123 distributor. I have the stock distributor I can swap back in but really hate having to go through all that again.
Symptoms don't seem indicative of a bad distributor based on what I've read on the interwebs. Anyone think this could be a distributor issue?

If the compression was bad, that would mean it would be doing this all the time instead of intermittently, right?

Bumping the thread to break the silence of the crickets.

I know you changed the relay board, but did you change the relays? I had the same exact symptoms and it ended up being a bad relay. Drove me crazy as I couldn't predict when or where it would cut out.

Thanks- yeah, and I verified the fuel pump is running even when it wants to stall.

Fuel filter or tank screen?

Replaced the filter last summer and haven’t put many miles in since. I refurbished the tank and replaced the screen several years ago, although I suppose anything’s possible.

When it stalls it seems to run ok if I keep my foot on the gas and the rpms over 2k. Drove back home on the freeway without any issues until I let off the gas. Seems like if it was stalling because of lack of fuel I wouldn’t be able to drive it at all or it would buck/hesitate every now and then.


.

I read thru this yesterday but can't remember if you've rechecked the fuel pressure recently?

Your critical inputs are your MPS (which You've been thru), CHT, TPS and RPM (distributor). I would go after the RPM next. As long as your fuel pump is still working and fuel delivery is correct and vacuum hoses and routing is correct then as you suspected, the distributor may be at fault. I think you should go that route and see what you find.

I don't have a gauge to test, but it's on the list of things to check. That said, if fuel pressure was an issue, I would expect to see issues when I am at partial load or WOT, and not at idle when fuel pressure is lowest, no?

Fuel pressure is constant on stock setup. Most newer fuel pressure regulators do lower pressure at idle based on manifold vacuum, but not our stock unit.

It's worth checking. Unfortunately you've run out of obvious and simple things to check. Now you need to make a list and check it twice...

having dealt with similar issue recently well actually a couple times in past few years, similar acting but - one time was the fuel pump, it was slowly going bad, I have a in line fuel pressure gauge now just for that reason, pressure should be constant if you can see if that pressure went down you have an issue with that pump or blocked screen or filter like mark and beatnavy says.
- the next time it was a MPS that was failing electrically - diaphragm not torn, held vac ok, but the MPS not always sending proper signal. I just don't think its your distributor but try the other one anyway. only make a change to one thing at a time. and as prevous person said, recheck everything again. all electrical and grounds. but I really think it may be with fuel supply/pump.

Ugh. Well today I eliminated the following 3 things from the shrinking list of possible causes for my car stalling:
Fuel pump: I verified pressure is at 29 both when it’s running and when it stalls.
CHT: swapped in a known good one (didn’t bother testing the one I took out)
Distributor: I thought this was the issue- removed the 123distributor and put in my old stock dist. Car stayed running long enough for me to think it was fixed. Verified the timing again, made slight adjustment to dial it in, car still running...got in and drove 6 blocks and it stalled as soon as I took it out of gear. As before, if it stays in gear and the car is moving (even when completely off the gas) it keeps running.

The only other thing I can think of is the old ignition wiring in the engine bay is bad somewhere.

Think about this. A loose connector or bad wire creates more resistance and thus heat when current runs through it.

Check all the primary circuts to the engine. Never read anything about the injector harness, ground points or ecu comnector.

I have 2 supposedly good ECUs, swapping them out hasn’t fixed the issue.
The wiring in the engine bay is original and old and a prime target for faults. I saved them for last because the cost of replacing the ignition harness and the injection harness is significant, especially in this time of income uncertainty. But unless someone has another idea, I guess that’s what next on the list.

That sucks, Robert. Sorry about the frustration. Several years ago I splurged and bought a new harness from Bowlsby. It may have prevent a lot of aggravation over the years.

I'm not using it currently. If you want I could possibly loan it out to you for testing purposes. It's got a couple of years of hard use on it, but it's still in good shape.

The only other thing I can think of is the old ignition wiring in the engine bay is bad somewhere.

I would look at this carefully.

Thank you! As always, I really appreciate your generosity. That said, I bit the bullet and will be ordering a new ignition harness from Jeff. Fingers crossed.

Given everything I've thrown at this car in the last few years it may just been cheaper to buy a running 914.

No problem, Robert. Boy I hope that wiring harness improves things. Definitely check ignition harness while you’re at it.

Good luck!

I have similar symptoms in my '74 2.0 EFI. This week, I changed all of the vacuum hoses, replaced and relocated the fuel pump to the front of the car (to eliminate the vapor lock issue), installed new fuel lines, and fuel filter, and the problem does not go away. The car is now idling closer to 1100 RPMs versus where I typically have it set up around 1000 RPMs. The problem seems to exacerbate after I run the car wide open in the highway going over 70 MPH for more than 20 minutes.

This is too strange, I also have the same problem with 74 2.0 Djet EFI. idle is about 1100, Runs normally after easy start up, intermittent stall problem is identical. AFter driving for 10 minutes, idle falls to zero, stalls out. Need to hold pedal to floor to get to restart. Exhausted all the typical remedies so took it to Porsche shop in Sac. They said the battery was not providing enough amp, replaced battery and idle seemed fixed, no stalls at stop. Now problem is back again. I have read the posts and cant figure it out.

Since I started this post, I'll give an update on where things are at, and also respond to the other two people who are having similar issues.

Got the new ignition harness from Jeff. A work of art. Installed it yesterday and spent an hour re-tuning the mps. I thought I had it dialed in, but I realized that at idle the AFR was way to rich at ~11.2. Although the part load AFR was good at ~13.5.
Maybe this was part of the cause of the stall all along? Maybe it was a combination of old wiring and an idle that was too rich? Maybe nothing is fixed and it just hasn't stalled yet?

So I'm back to trying to dial in the AFR and the problem I'm running into now (what what I ran into before) is when I set the AFR set for partial load (~13.5) using the MPS inner adjustment screw, the the idle AFR ends up being too rich (~12.5).
So I then try to lean out the idle AFR using the throttle body air bleed screw and the ECU adjustment knob to a point where the idle speed is at 900-1000k and doesn't hunt, but that puts me at 12.7 at best. I see others at 14+ AFR at idle.
What am I doing wrong here?

As far as the others who are having stalling issues... start a new thread.
I say that not to be a jerk, but because there's a lot of potential causes that you are seeing similar symptoms, and going through them all will not only derail my thread but it will make it harder to troubleshoot your particular situation.

I have to share my recent experience as I include a couple different aspects but identical symptoms. '73 2.0 all stock with Pertronics 2....I think the smog idle device (afr?) is removed. So after many vapor lock issues moved fuel pump up front and problem disappeared. I drive maybe 3-4,000 miles a year...maybe 5,000. So car has worked perfect and routinely for last couple of years but a month ago started to do the low idle no start when warm routine. I discovered a broken wire on the temp sensor on top of the plenum (temp sensor 1 I believe) and repaired it. I also have a throttle body cleaning machine, BG Products, and did the cleanse as well. After I clean the throttle body I can hear the idle adjustment screw much clearer and usually have to turn the idel down. I think these cars like a really clean throttle body. Car ran like a jet and started perfect so I thought I was out of the woods. I accidently pulled the cold start injector plug out upon re-assembly and car would not start next day and I missed the recent SoCal ride. Anyway cars seems all cured now. Hope that offered something.
All the best to all,
gg

So I was able to drive around for an hour last night, constantly stopping to adjust the MPS which means there was a fair amount of idling mixed with short drives, engine always running. That equals a very warm engine and there was no stalling.

Just took it on the freeway for 20 minutes, AFR at a steady 13.5 while cruising and as soon as I get off the freeway it of course stalls again. I’m typing this in a parking lot 30 miles from home hoping the car will make the drive back.

I’m almost out of things to try. My car has become a paperweight just in time for summer again.

_____

**Update**
I let it sit for 15 minutes or so and it started right up and idled just fine. Made the trip home and it stayed running when I pulled into the driveway.

Back to basics: Air, fuel, spark, compression.
Under what conditions for any of the four categories above would allow the car to keep running fine with my foot on the gas with no <apparent> lack of power but stall when off the gas?

Air seems an easy one to take off of the list.

Fuel: Lines are new and good and new filter. Verified that the fuel pressure stays in spec even when the car wants to stall. Bosch fuel pump is mounted in the frunk and has less than 1000 miles on it. Injectors sent out for cleaning and are within spec. New injector seals.

Spark: New ignition harness. Tried both stock and electronic distributor. Tried both stock and new coil. NKG plugs and wires have less than 1000 miles.

Compression: Haven't checked, but car has good power and compression isn't an intermittent thing, right?

All vacuum lines replaced, new plenum hoses, intake gaskets, TB gasket, and NOS TB. Verified no vacuum leaks (including plenum). Tried 2 different MPS (both hold vacuum).
New CHTS, also tried swapping with old one.
Swapped relay boards (connections tested good on both of them).

ECU is next on the list to swap out. (I may have already tried this, but I can't remember).

maybe i missed it but have you tested the electrical connections on the MPS?

You can send your extra ECU to Fuel injection Corp in Tracy california and they will test if for free.

Also triple check your grounds including the trans to body.

On a project car we ran into some fuel line that collapsed after a couple months of sitting full of fuel. Lucky we found it while still working on the car or that would be an area that we would not have thought to check since it was new.

Grounds are good from injection harness and I have a newer trans to car body strap.
New fuel lines
Tried 2 different MPSs
I haven’t tried swapping the ECU yet- I have a spare so that is next.

have you tested either of MPS electronics? Vacuum is only part of the equation
you are going to keep going in circles if you do not start from the very basics and systematically check off everything even the items that you say are new but they are not new since after the problem started.
Those are my thoughts