1974 1.8L engine fast idle then stalls, Fuel injection issues Options

[Van B]

Wonkipop, you meant open on the AAV when you put it in the freezer. Then closed when it warms up. Even if the heating element is bad, this AAV is still good about closing when the engine warms it up. But the spring does get tired and won’t open all the way anymore… unless it’s gummed up.

Otherwise, based on the neglect while sitting for years. I guarantee the injectors aren’t working either. Bad spray pattern or too clogged to increase flow are very probable issues.

But what I said in post #120 is still my opinion.

[wonkipop]

Wonkipop, you meant open on the AAV when you put it in the freezer. Then closed when it warms up. Even if the heating element is bad, this AAV is still good about closing when the engine warms it up. But the spring does get tired and won’t open all the way anymore… unless it’s gummed up.

Otherwise, based on the neglect while sitting for years. I guarantee the injectors aren’t working either. Bad spray pattern or too clogged to increase flow are very probable issues.

But what I said in post #120 is still my opinion.

ah sh$t.

sorry. i meant that. dyslexic today. (IMG:style_emoticons/default/biggrin.gif) (IMG:style_emoticons/default/biggrin.gif)

i agree with post #120.
and more.

[tshih914]

@wonkipop

The ECU was not left dangling loose in the engine bay. It was securely mounted to the rubber mat on the firewall by a long screw into the firewall so I believe it is not damaged.

I did notice the CHT was very rusty and probably needs to be replaced. I think it is a thermocouple resistor that register about 300 ohms when cold and resistance goes down when hot. Checking it is just a matter of measuring the resistance at the two ends (head of the part that screws into the cylinder head and tail of the wire leading to the ECU harness)

I have received the hose kit and am in the process of removing the AAR and cold start valves for testing and cleaning. That hose kit does not seem to have the right number of hoses or some of which are too short to replaced those currently in my car.

[wonkipop]

@wonkipop

The ECU was not left dangling loose in the engine bay. It was securely mounted to the rubber mat on the firewall by a long screw into the firewall so I believe it is not damaged.

ok thats good about the ECU.
makes me look less sceptically at it in photos. (IMG:style_emoticons/default/biggrin.gif) (IMG:style_emoticons/default/beerchug.gif)

sounds like you got a bit of momentum up now.
good luck with testing and checking all the bits.

did the hose kit come with a guide drawing for each hose?
would be unlike AA to have that wrong i think.
list up anything specific you encounter with a photo and perhaps we can check it against what should be there and where they go.
you will find my hand drawn hose diagram is accurate, its off an original cond car. (IMG:style_emoticons/default/beerchug.gif)

[wonkipop]

@tshih914

you might wonder why i am touchy about ECU's

a little story.

got a friend of sorts who owns a late 90s BMW M3.
who has had a saga that has lasted 5 years.
for some reason two decades ago he bought one of the so called "clutchless"manuals.
early tech.
not a paddle shifter on steering wheel but you flick the gear lever version.

anyway.

it started sh#tting itself after you shifted gear.
went into 3 cylinder limp mode.
for a while he got away with switching it off and restarting.
but it just got worse.

when the BMW "i am a cripple" business started, our resident mechanic mike,
said - "its the ECU".

the owner grinned and decided not to take the advice.

5 years later, having done everything, and having taken advice from every dickhead under the sun, at the BMW club, the alfa romeo club etc and so forth, having replaced oxygen sensors, rebuilt the vario cam unit whatever its called on a BMW, etc etc etc etc - having searched every BMW forum on the globe to get opinions, he finally found another BMW "REAL expert" from the era who was retired. guy said the same thing as mike.

"ECU mate"

and then he contacted BMW to get one.

they said. "lucky fer you mate, ve haff vone left".
one in the entire world.
(because its a special ECU for the dumb arse flick shift clutchless manual).
rare as hens teeth because no one else was stoopid enough to buy them.
most sane punters bought the three pedal fully analogue version.
its better.
but don't say that to my "friend".

anway - so he got it. all special delivery from germany.

and some tech experts here at a special BMW workshop hitched it up to his engine and did some keyboard work etc and.......it goes.

but thats it. he is farked if it happens again. there are no more ECUs for that pile of bavarian excrement. (please excuse my negative opinion of german gum tree magnets).

---

in short what the original ECU was doing was cutting to 3 cylinders to accomplish the shift, because thats how high tech its low tech was. but then it could not reconnect to all 6 cylinders after the shift. so it was stuck in the zombie world of half way through a gear shift.

----
now a 914 ECU was built to survive on the surface of the moon. its seriously over-engineered. military grade. but its half a century old. i'm sure bosch would be both astonished and smug at the same time that these things are still going.
but you know the older they get the less tempted we should be to subject it to conditions equal to a straffing pass on an afghanistan mountain hide out for el quada or a bomb drop on bagdad. (IMG:style_emoticons/default/smile.gif) (IMG:style_emoticons/default/biggrin.gif) (IMG:style_emoticons/default/beerchug.gif)

[StarBear]

(IMG:style_emoticons/default/popcorn[1].gif)

[Van B]

The ECU is very obviously not mounted to a rubber mat, on a firewall, with long screws.

[tshih914]

The ECU is very obviously not mounted to a rubber mat, on a firewall, with long screws.

I went to check the CHT sensor (which is really difficult to get to buried under engine tin near spark plug #3) Just measured the resistance from the connector rectangular plastic piece to engine ground and it read 1.77kohm. I don't know what that means as I expected around 300 ohms cold. Will check once the new part comes in from Amazon.

The next thing I did was to remove the AAR and sure enough the valve is open when cold. However when I connected 12V to the 2 pins at the connector after 13-20 min the valve felt warm to the touch but the opening did not close so that valve is broken.

Also in looking at the valve there appears to be a post for grounding wire/connector? that was not attached to anything.

[tshih914]

The ECU is very obviously not mounted to a rubber mat, on a firewall, with long screws.

I went to check the CHT sensor (which is really difficult to get to buried under engine tin near spark plug #3) Just measured the resistance from the connector rectangular plastic piece to engine ground and it read 1.77kohm. I don't know what that means as I expected around 300 ohms cold. Will check once the new part comes in from Amazon.

The next thing I did was to remove the AAR and sure enough the valve is open when cold. However when I connected 12V to the 2 pins at the connector after 13-20 min the valve felt warm to the touch but the opening did not close so that valve is broken.

Also in looking at the valve there appears to be a post for grounding wire/connector? that was not attached to anything.

[StarBear]

Might want to squirt a few drops of silicone spray in there just in case that loosens things up a bit. Worked on mine which was mostly working but needed a little encouragement to behave. (IMG:style_emoticons/default/biggrin.gif)

[tshih914]

[quote name='tshih914' date='Mar 11 2023, 11:59 AM' post='3064228']
[quote name='tshih914' post='3064219' date='Mar 11 2023, 11:03 AM']
[quote name='Van B' post='3064146' date='Mar 11 2023, 06:29 AM']
The ECU is very obviously not mounted to a rubber mat, on a firewall, with long screws.
[/quote]

The photo was taken after I had removed the ECU to check the TPS and wiring and have discarded the rubber mat.

The fact that in one of the test where I pinched off the hose from the AAV to the AFM caused the RPM to drop from 3000 to around 1500 suggested that the AAV had been stuck open even after the engine had warmed up. I looked on Ebay and found a used AAV (for 75-79 VW bbeetle) with same Bosch part # 0280140101 for $80. Should I get it?

[wonkipop]

ok @tshih914 .

thats good affirmation re the AAV.
combine that with your errant decel valve and you probably pretty much have the source of uncontrolled metered air that were likely significant contributors for the elevated "idle".

as @StarBear suggests you could see if you could coax the AAV to life.
the AAVs are hard to find these days.
if you cannot bring it back to life there are ways to deal with it.
it is useful for cold start.
and some members like @emeryGT350 have rigged manual taps in to the hose to the air inlet tube so they can switch it out of the air feed circuit after its done its job for 5 minutes at start up,
you may have to rig something like that up so that you can use it for the cold start and then once the engine is warm take it out of play. you want it to be able to be closed once you get to the point of tackling a stable warm engine idle.

(IMG:style_emoticons/default/beerchug.gif)

as to the one on ebay.
i would communicate with the seller and ask if he can reassure it actually works.
maybe some photos that document a test of it open and closed or something.
you don't want to lay out $80.00 on just another screwed AAV.
they are all old and tired at this point in time unless somehow one thats been in a box sealed in plastic for 50 years.

[StarBear]

AAV FS in classified FS/WTB forum, as Van B highlighted. $65. Unsure if working?

[wonkipop]

@tshih914

you mean this arrowed.
its just an engine tin screw and washer.



the technique for how to get the CHT out is in the factory manual.
it could be tricky if its never been out like all things are that are in threads and have never been undone for half a century.

mine worked so luckily i did not have to remove it. (IMG:style_emoticons/default/biggrin.gif)
i think @Van B did take his out and replace it.
he might have some tips if you are lucky.

[Van B]

Fixing the AAV is not going to make the car take throttle. And a full open AAV will not make the car idle at 3k. I bought one for a BMW that is slightly bigger than stock and it gives me a healthy 1500rpm cold start idle.

Further the heating element cannot completely close the AAV. It still needs engine temp to get hot enough to close. The heating element provides a good head start so you don’t have 10min of full high idle.

With age and heat cycles, the spring gets lazy and the part neither opens or closes fully. They also get carbon deposits over the years that can gum them up at the disc.

[Van B]

Likewise, the CHT will not cause the car to die when you touch the throttle. But to remove it, coil the wire around the screw driver so you can fit it inside a deep socket, slide the socket over until seated, then attach the ratchet. Conversely, you can cut a slot in a socket like an O2 sensor socket.

[wonkipop]

Fixing the AAV is not going to make the car take throttle. And a full open AAV will not make the car idle at 3k. I bought one for a BMW that is slightly bigger than stock and it gives me a healthy 1500rpm cold start idle.

Further the heating element cannot completely close the AAV. It still needs engine temp to get hot enough to close. The heating element provides a good head start so you don’t have 10min of full high idle.

With age and heat cycles, the spring gets lazy and the part neither opens or closes fully. They also get carbon deposits over the years that can gum them up at the disc.

i believe it was the combo of AAV and decel that was giving the full 3000?

once he clamped off decel it did drop significantly.
and similarly when he clamped of AAV.
not sure he did them both together.

also clamping still lets some air through the hoses.
to really take them out the test has to be done with hoses out and plugs in.

also you can get excessive air leaking past the throttle plate around its edges if its not adjusted properly on its stop. will also pull the flap on the AFM.
that can contribute a portion of the high idle. but i wasn't going to go there just yet.

i agree not taking the throttle is not likely about these things.
a further matter that is aside from these things.
even mike was not sure about that, saying, well......it could be lots of things.
then repeated the mantra. valves have to be adjusted. timing set.... etc.

that is true about the electric current not doing it completely for the AAV.
i noticed that about mine when i tested it a few years back.
it did shut but not completely.
i showed it to mike at the time and he said, yep thats ok. said no more.
but it certainly shut to a significant degree.
if this ones not moving under electric current at all it would tend to say it needs some attention and love to see if it can be raised from the dead.

[wonkipop]

these are the test values for the CHT.
again from the factory manual.
its in there you just have to look for it.
it can be a bit all over the place finding the stuff as some information gets mixed around with the D jet stuff.



yours might be alright? if you got 1.7 k ohm.
i guess it depends on how cold it is there currently where you live.
at 68 F it says you should get 2.5 K ohm.
and progressively less for colder temps.

[technicalninja]

yours might be alright? if you got 1.7 k ohm.
i guess it depends on how cold it is there currently where you live.
at 68 F it says you should get 2.5 K ohm.
and progressively less for colder temps.

Think you have it backwards...
With NTC thermistors resistance decreases as temperature increases.

I will slope a NTC sensor. Put it in freezer, record resistance, refrigerator, record, room temp, record, hot tap water, record, boiling water, record.

I want the slope between each point to be similar for all...

Sometimes you will find a sensor drops out at a certain temperature.

[wonkipop]

@Van B

this is his report that interested me.

it was clear from the photo that the AAV was still connected.
idle screw as out two full turns as you had suggested.

revs were now down at 2,500 from 3,000.
not attempted to do the further steps we suggested.
1) block off the AAV after the engine had warmed.
2) adjust the idle screw to see if he could lower idle revs.



it seemed to me the engine was able to act a little in that narrow 500 rpm range.
it depends how gentle he was opening the throttle.

can you see where i am going?

what i want him to do is get the engine to idle revs i he possibly can.
or a steady lower idle.
if he can what i would want to do is gently manipulate the throttle.
very gently.
see if it will rev to 2000.
if it does.
see if it will rev up to 3000. (we know it can run there and off the AFM flap too).
if does.
gently take it over 3000.
see what it does.
each step taken gently, not just stabbing of the gas pedal.

i'm going to dig up some diagrams i thought i had on the AFM and connections from potentiometer to plug.

so far all his electro vac / sensor components are checking out.
assuming valve adjustment and setting of timing (which can be done at idle) he should be able to get this thing to idle at lower revs with if the decel is kept out of it and the AAV is closed when its warm.

it may not be what i am thinking of.
in which case? have to think again!