‘74 1.8L L-Jetronic Cold Start Low Idle, Mystery solved! Options

[Van B]

I want more air through the Aux Air Valve… as in a bigger valve. I would rather see a cold start idle similar to what I have on my 996. 1500RPM is a good speed to get all the oil circulating and still low enough that you’re not really putting a load on the engine.

[wonkipop]

I want more air through the Aux Air Valve… as in a bigger valve. I would rather see a cold start idle similar to what I have on my 996. 1500RPM is a good speed to get all the oil circulating and still low enough that you’re not really putting a load on the engine.

i did the cold start test today with the tank top off of fresh gas.
guess what.
no idle stumble phase between minute 2 and 3.
it kind of went down after 2 minutes and was lower for a minute and then came back up and warmed up. but no nearly dying thing.

gas goes off, even after only 3-4 months? enough to upset the old 1.8
a 356 bloke i was talking to recently told me that modern gas drops octane faster than gas even 10 years ago.
we don't have the E gas stuff down here so that is not the cause.
its just modern petrol.

i can blame that bit of the cold stumble on dickhead dan?

[StarBear]

I want more air through the Aux Air Valve… as in a bigger valve. I would rather see a cold start idle similar to what I have on my 996. 1500RPM is a good speed to get all the oil circulating and still low enough that you’re not really putting a load on the engine.

i did the cold start test today with the tank top off of fresh gas.
guess what.
no idle stumble phase between minute 2 and 3.
it kind of went down after 2 minutes and was lower for a minute and then came back up and warmed up. but no nearly dying thing.

gas goes off, even after only 3-4 months? enough to upset the old 1.8
a 356 bloke i was talking to recently told me that modern gas drops octane faster than gas even 10 years ago.
we don't have the E gas stuff down here so that is not the cause.
its just modern petrol.

i can blame that bit of the cold stumble on dickhead dan?

I sort of saw that a few years ago but with maybe 6-month old gas, despite having stabilizer added to it. Since then have been using premium 93 octane as I don’t drive it a lot so extra $ not a big issue. Been driving it more this year, too, so gas doesn’t get stale. Helped stop the knock at low driving rpm, too.

[Van B]

I don't really have a process for the 914, but in my 996 I added some race gas on every fill-up. That stuff always has good stabilizers in it and its worth a few extra ponies. One addendum though, you gotta avoid the oxygenated race fuels. I'm talking the old school highest octane you can get for unleaded.

[Van B]

Just did a little test and I figured I would report my findings.

I pulled the AAV out and bridged the tubing from intake boot to plenum. The car fired up instantly from completely cold and jumped to 1500RPM!
Things were looking promising but just a few seconds later I started to get what looked like a runaway situation. The revs climbed up to 3500RPM so, I put my hand over the intake snorkel to choke it down. I let it fall to <1000RPM and then uncovered. The revs then climbed back up to 1500-1600RPM and stayed there.
However, I did notice the engine was rich and I could make out a little black smoke amongst the condensation from the exhaust.
I gave the throttle a rev to clear it out and then killed it.

As a result, I have yet again inspected the AAV, but can’t see anything wrong. Movement is free, spring tension is consistent, and it is totally clean.

So, the only thing I could see is that when I pulled it from the car, while still cold, it wasn’t quite fully open, but was close. The opening is not real large even at full opening, but that last little bit could be considered the most important since it’s part of the full ellipse shape and not the triangular (closing) side.
I’m going to leave it in the freezer for a couple hours and see what it looks like then.

My thoughts from this little experiment are that full pipe diameter is too much so, the restrictive shape of the AAV makes more sense to me now. But, and this is my hypothesis, if the spring has fatigued, I’m not going to get max flow through the valve.

Further, somewhere less than full tube size and current AAV aperture I’m getting now should be a proper high idle.

I guess I’ll see what I learn from the freezer.

Van

[StarBear]

(IMG:style_emoticons/default/smile.gif) Onward!

[wonkipop]

Just did a little test and I figured I would report my findings.

I pulled the AAV out and bridged the tubing from intake boot to plenum. The car fired up instantly from completely cold and jumped to 1500RPM!
Things were looking promising but just a few seconds later I started to get what looked like a runaway situation. The revs climbed up to 3500RPM so, I put my hand over the intake snorkel to choke it down. I let it fall to <1000RPM and then uncovered. The revs then climbed back up to 1500-1600RPM and stayed there.
However, I did notice the engine was rich and I could make out a little black smoke amongst the condensation from the exhaust.
I gave the throttle a rev to clear it out and then killed it.

As a result, I have yet again inspected the AAV, but can’t see anything wrong. Movement is free, spring tension is consistent, and it is totally clean.

So, the only thing I could see is that when I pulled it from the car, while still cold, it wasn’t quite fully open, but was close. The opening is not real large even at full opening, but that last little bit could be considered the most important since it’s part of the full ellipse shape and not the triangular (closing) side.
I’m going to leave it in the freezer for a couple hours and see what it looks like then.

My thoughts from this little experiment are that full pipe diameter is too much so, the restrictive shape of the AAV makes more sense to me now. But, and this is my hypothesis, if the spring has fatigued, I’m not going to get max flow through the valve.

Further, somewhere less than full tube size and current AAV aperture I’m getting now should be a proper high idle.

I guess I’ll see what I learn from the freezer.

Van

great experiment mate (IMG:style_emoticons/default/beerchug.gif)

i can remember mine 30 years ago as a 15 year old car. and it started up and idled fast.
maybe not 1500, but i seem to remember around 1200. could be a faulty memory, its a long time ago. but it def. started at a faster idle and came down.

looks like the AAV is a very finely tuned thing and it does not take much to get out of synch and not be just right?

as to gas. we can get three grades here. 91, 95 and 98. i've been running 95.
i might start using 98. might keep it fresh for longer. the 356 man said he had really noticed the gas going off faster for the last 5 years or so. similar problem, doesn't drive his car enough.

mine runs rich during that first warm up phase. same as yours. can see it in the exhaust and even what is being spat out in the moisture. the mechanic who helps out and looks after things no doubt observed that. probably why he was pretty sure i was the AAV? means the ECU and sensors 1 and 2 are still working close to correctly and its enriching the mixture.

[Van B]

We use RON+MON/2 here in the states. That’s why our octane numbers are lower. Motor Octane is a much lower figure than Research Octane so, it drags the average down.

[Van B]

Just a short update for the record:
I had noticed that on the two times I’ve driven the car at night, it would almost refuse to idle until completely warmed up. So, on a hunch, I thought maybe the voltage regulator was causing some faulty signals. There are definitely classic symptoms like dim lights at idle etc. So, after screwing up and buying a cheap replacement that didn’t fit, I spend $200 on a Bosch solid state.
Started did a cold start as soon as I installed it, no change. Man this thing struggles when cold…

I’m starting to get frustrated. And doubly so that there’s no L-Jet expertise around here. I suppose I’ll just throw parts at it for a while and see what happens. Nothing is broken so, I’m thinking there’s a possibility it could be a collection of parts that aren’t working properly.

[wonkipop]

had that very chat today over lunch with mike.
he still says its the AAV and its degradation is in combination with the retarded idle. early smog stuff.
its a crude device compared to modern cars.

he had an interesting suggestion to me which was try a cold start with the aav unplugged (electrical connection) and see what it does. eventually it closes due to engine heat but that will stop the electrical coil heating and closing it. this was not as a solution, but just to see if maybe he was right.

i might try it as an experiment.

now that its warmer here (real hot today) mine is starting and warming up quickly. but not with a faster idle. the aav is effectively a choke. and i remember the auto chokes on twin carb vws were pretty much on the blink and uneven side to side after a mere 10 years. i had them unplugged back in the day and just used to sit there and warm it up until it would idle rather than deal with auto chokes. i had them wound off.

--------

i was getting the low down from mike on why vw would have disconnected vacuum advance for california. his view was it was another crude way to meet californian emissions by always slightly retarding the engine at cruise and as you came off throttle.
a trick to burn just enough hydrocarbons in the exhaust and not make too much NOx to pass the lab smog test. "crude" because they were adapting the behaviour of the double can distributor that was more ideal for the 49 state cars. ie cheap.

[wonkipop]

there is probably only two other things that can influence things.

the cable and air cooling flaps affair.
i am guessing you have already worked through that?

and there is a temp sensor in the AFM that reads incoming air temp.
the procedure for testing that is in the manual you have downloaded.

the other possibility is minor sources of air leakage around the throttle body bearings.
if its leaking there the AFM can't measure it.
only a small leak but could be there and everything gets tighter as the engine warms up.

[Rob-O]

I've kinda been lurking this thread for awhile now. I've been meaning to reply but have been busy.

I've got a '74 1.8L L-Jet car. When I got the car it was running the dreaded one carb setup. I sourced all the L-Jet parts and then reinstalled on my vehicle with lots of help and guidance from Clay, who lives fairly close by.

I had a low idle when cold for a long time. I won't go into everything I did to get my FI running well but thought I'd offer a piece of advice. I think you're focusing too hard on the AAV. If you've tested it and you're confident it's working then I'd move on. Personally I tried to isolate as many systems or components as I could. So for me, I removed the decal valve. I may put it back at some point when I have the time to properly test/adjust it but at the moment the car runs well without it.

I also tried to isolate the vacuum canister on the distributor. I mean, it's great for advancing or retarding the timing when it's running correctly but if there are any issues in that system it's going to cause high idle, low idle or a hunting idle. What I did was to remove the vacuum lines from the throttle body and cap off the lines. That way I felt that I was vacuum leak free as far as the lines to and from the canister. But even after I did that I still had idle issues. The vacuum canister seemed to work (when I vacuum tested it). But it wasn't until I removed the clip from the arm that attaches to the distributor plate that the issue was resolved. This was all AFTER I removed the distributor and cleaned and regreased the advance plates to ensure that they were moving (they weren't initially).

So, if you're confident that you've cleaned up the vacuum leaks on the car and everything mechanical is up to snuff, you may want to start isolating other systems like the distributor. It could be the source of at least some of the issues. I would:

1. Clean/relubricate the distributor advance plates. When you grab the rotor with the distributor in the car you should be able to turn it a few degrees. If you can't the advance plates are most likely gummed up and not allowing the weights to move as they should (and most probably they're stuck 'closed' to they don't swing out as the distributor spins).

2. I would test the vacuum canister to ensure it holds vacuum. Even if it does, I would still highly consider removing the clip that holds the arm of the vacuum canister to the advance plate (or remove the canister altogether and cover the hole left behind). Cap off the lines at the throttle body would be best but I suppose just capping the vacuum lines would work too. By doing that you're ensuring that the canister has no effect on the advance or retard of the ignition.

3. Examine cap/rotor/points/condenser (didn't see if you had moved over to something like Pertronix) and the rest of the distributor. I don't have information on the amount of play allowed in the distributor gear but you may want to look that up. My guess is that isn't the issue because excessive play there seems like it would cause a hunting idle. Reinstall the distributor. Then time the engine. Timing should be a breeze because you don't have any vacuum lines to remember to connect/disconnect.

[Van B]

You definitely been saving up your posts lol! I’m gonna take this in line with your post because there are just so many things to discuss here!


I had a low idle when cold for a long time. I won't go into everything I did to get my FI running well but thought I'd offer a piece of advice. I think you're focusing too hard on the AAV. If you've tested it and you're confident it's working then I'd move on. Personally I tried to isolate as many systems or components as I could. So for me, I removed the decal valve. I may put it back at some point when I have the time to properly test/adjust it but at the moment the car runs well without it.

I mostly agree here, I think the one recent test where I bypassed the AAV and got a super high idle on cold start is an interesting result and leaves that door open. Also, I cracked the code on the decel valve on a different thread. I had high idle issues when I bought the car and came to realize that the decel valve needed to be adjusted. Opening vacuum greater than 20 in hg makes the valve work like a champ.

I also tried to isolate the vacuum canister on the distributor. I mean, it's great for advancing or retarding the timing when it's running correctly but if there are any issues in that system it's going to cause high idle, low idle or a hunting idle. What I did was to remove the vacuum lines from the throttle body and cap off the lines. That way I felt that I was vacuum leak free as far as the lines to and from the canister. But even after I did that I still had idle issues. The vacuum canister seemed to work (when I vacuum tested it). But it wasn't until I removed the clip from the arm that attaches to the distributor plate that the issue was resolved. This was all AFTER I removed the distributor and cleaned and regreased the advance plates to ensure that they were moving (they weren't initially).

I just bought a timing gun a couple weeks ago so… distributor and timing is still a lost art to me. My grandfather died in 1997 and that was around the last time I ever timed a car. That said, this one is pretty straight forward I think. I don’t know what clip you’re talking about. Haven’t seen anything like that.
Regarding disconnecting lines, I tried that and the car wouldn’t cold start at all from cold but started fine when warm. That was all documented a few pages back.

So, if you're confident that you've cleaned up the vacuum leaks on the car and everything mechanical is up to snuff, you may want to start isolating other systems like the distributor. It could be the source of at least some of the issues. I would:

1. Clean/relubricate the distributor advance plates. When you grab the rotor with the distributor in the car you should be able to turn it a few degrees. If you can't the advance plates are most likely gummed up and not allowing the weights to move as they should (and most probably they're stuck 'closed' to they don't swing out as the distributor spins).

My distributor turns real easy. If anything, I wish it would clamp down a little tighter. Last time I torqued on the distributor after clamping everything and with the timing light I could see that timing would still move a bit as I applied force.

2. I would test the vacuum canister to ensure it holds vacuum. Even if it does, I would still highly consider removing the clip that holds the arm of the vacuum canister to the advance plate (or remove the canister altogether and cover the hole left behind). Cap off the lines at the throttle body would be best but I suppose just capping the vacuum lines would work too. By doing that you're ensuring that the canister has no effect on the advance or retard of the ignition.

I’ll put the mighty vac on there and see if it holds. And like I said, I already failed at the no retard set up.

3. Examine cap/rotor/points/condenser (didn't see if you had moved over to something like Pertronix) and the rest of the distributor. I don't have information on the amount of play allowed in the distributor gear but you may want to look that up. My guess is that isn't the issue because excessive play there seems like it would cause a hunting idle. Reinstall the distributor. Then time the engine. Timing should be a breeze because you don't have any vacuum lines to remember to connect/disconnect.

Haven’t taken the distributor apart and I think I’ve beat the vacuum line thing to death, but I’m sure it’s standard points

In the end, I think the main point to your post is the one you didn’t expand on. You had a partner in working through all this. This is what I just posted about too. I’m frustrated. If [b]@Wonkipop was a few thousand miles closer, I’m sure we’d have made some serious progress. But I’ve asked for shop recommendations for my area and just got chaff…. “You don’t need a shop, this forum has all the info, blah blah blah.” This forum is great, but it’s just a forum.[/b]

Van

[wonkipop]

to expand on the AAV a bit.
and i realise that rightly @Rob-O has cautioned not to concentrate too much on it.

most of my components are not overly worn.
and i thoroughly checked out the distributor on mine 2 years ago - its good.

i think Rob-O is on to something when you are looking at a higher mileage greater used car. a lot of the components are suffering wear - or as the germans say. "its vorn".

i did manage to find on Ratwell's site, which is very good, some info on the AAV.
its supposed to take 5-6 minutes to do its thing.

the trouble with the AAV is knowing just how open its supposed to be at cold.
and then trying to accurately time the closure. i think mine was doing the whole thing a bit faster than 5-6 minutes. but when i tested it i wasn't really timing it or looking at it closely enough. i was just giving it a rudimentary test to see if it worked. i had not found any information around parameters back then.

my reason for focussing on it in the case of mine is i buy the theory that the heating strip in it is delicate and weakens over time due to repeated heating. to my way of thinking that means not only does it close too quick, but it also maybe is not holding the appature wide enough open at cold.

trouble is there is not much you can do about it, other than clean it.
i did find a 924 thread where a young guy had taken one apart and thoroughly cleaned it. he did note though there is not much you can do about a weakened heating metal element.

Rob-O' suggestion while good do seem to involve basically knackering the whole warm up system in a way. something i am reluctant to do.

its very sound advice to go right over the distributor and make sure its all operating sweetly.

[emerygt350]

He was describing movement on the advance/retard plate in the distributor, not whether the whole thing rotated...

[wonkipop]

from what Van is describing it does not sound like his distributor is suffering from sticking advance retard pull arm (or plate as you refer to part of the same mechanism emery).
the reason i say that is you would feel that as you pulled away from stop and idle.
hot or warm. the engine would hesitate or stumble as it tried to come off the retarded idle.

but it sure doesn't hurt to go through the distributor.

van has a new CHT. and it works. so the cylinder head temp sensor is AOK

i tend to think the other sensor in the AFM is probably ok, it measures incoming air temp and does influence the mixture. it can be checked, there is something in the manual i seem to remember. if not it is in another L Jet manual i have.

what he is doing is the right way to do it. one thing at a time and tick them off.

i admire the will to make a 50 year old "automatic" clock work device behave as it should and i get why he wants it to do it. just get that engine up to heat and cut down that wear and tear.

its making me want to do it with mine.


i have a friend here, her grandfather was a mechanic and her father ran a holden dealership. together they won the bathurst 500 in 1968 in the devils number monaro (#13). her grandfather used to build exquisite clocks in his spare time to relax.
this warm up thing with a 1.8 is like clockwork but its not done with gears. but its a form of clockwork. its a timed affair in which something is possibly getting out of whack, because it all comes good once it is actually warm.

EDIT.
@Van B.
i suspect its going to be difficult to find someone to sort the problem there in terms of a shop. its tough enough here. "where is the port to plug the lap top in?".

i am about to give mine a bit of a concentrated dose of attention. i spent the first three months of this year rebuilding the original bosch fuel pump after being told it was impossible. turns out its not if all that is happening is all the seals are leaking fuel.
it was harder than i thought but it was doable. so i've got to get it up on hoist and generally disable it for a while and go through it. i'm going to tackle some of this stuff physically then instead of mental thought bubbles.

[emerygt350]

It's been ages, so you might have done this already, but have you put a vacuum gauge on it?

Have you verified you are at the correct timing? Again check that the distributor is working correctly. Don't fear the distributor, super easy to pull out and clean/lubricate.

[wonkipop]

i've gotten this far with the idea of rebuilding my AAV.
i'm trying to work out if i can do something to renew the resister strip/spring as well - this kit does not cover that.
i've just got to check i can get the right interior rebuild and if this is it.

what i want to do is get hold of another AAV to do it to rather than the one i have.
and there in lies the problem for now. there is a SAAB wreck lying around i have not got under the bonnet of yet. its a 74 but its D=Jet so i don't think i am going to have luck there. though i did get a spare (and now functioning) bosch roller cell fuel pump off it.

i've struck this before with the europeans that there are all sorts of rebuild kits that guys in france and germany have come up with. particularly so with citreons where some electric components and small pieces are getting very hard to get. no choice but to rebuild.

https://www.ebay.com/itm/185166067358?_trkp...7Cclp%3A2047675

[wonkipop]

attached some stuff for @Van B.

first.
testing temp sensor 1. located in the AFM. this measures temp of incoming air.
(i think its unlikely to be the problem, but why not test, takes no time).
v has already replaced temp sensor 2 (CHT sensor) so that one is good.






the warm up for L jet is in the end very simple.
AAV is like sitting there with the throttle cracked open.
moves the AFM flap - basically that makes the engine rev. kind of that dumb.
yes - there is some other stuff going on, enrichment of the fuel mix while the engine is cold. but as far as i can tell that is down to the two sensors. 1 and 2.
(i think this is why my mechanic keeps coming back to the AAV with me).

the ECUs are built like tanks, survive a nuclear war.
the damn things are still functioning after half a century.
its lunar module spec. so the routine in there is likely to be completely intact.

the AAV is adjustable. there is a nut on the back of it. there is about 1/8 inch adjustment. they can be played about with that much. you can take them apart, and you can clean them if you want to go all out. if you don't want to take them apart you can try the clean with carb cleaner or seafoam through the open hose connection ends.

this is what i shall be concentrating on first with my weak cold idle.
just making sure i believe that AAV is in correct order before digging deeper in mine.

i will probably have more luck sourcing an old AAV from the USA to pull completely apart than i would here. maybe some old volvos lying around have the AAV. more likely candidate than junkyard datsuns (all carbed here from that era).





the AFM flap itself is also a good candidate for checking.
make sure it is able to move that first little bit freely and its not sticking.
that could also be screwing with things.
ie the AAV can't suck the flap open.
its not moving much for that fast idle phase.

[Van B]

It's been ages, so you might have done this already, but have you put a vacuum gauge on it?

Have you verified you are at the correct timing? Again check that the distributor is working correctly. Don't fear the distributor, super easy to pull out and clean/lubricate.

Yup. There’s only one mark on this engine. Done it three times now as one was the experiment to mimic the California setup… didn’t work. I’ve also confirmed that I get 30 degrees of advance at 3k RPM.
I’m not pulling it because it’s operating as it’s supposed to. But also, I would prefer to have someone who can show me how all the bits work as opposed to blind exploration.

I will put a vacuum gauge on both ports this weekend just to confirm there are no leaks.