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

[emerygt350]

Pull it off the air cleaner and cap it with your thumb. If you can feel it sucking then you know it is working.

[Van B]

Pull it off the air cleaner and cap it with your thumb. If you can feel it sucking then you know it is working.

Yeah, I can play little dutch boy too. First will be some forceps on the short line. Prior to my first crank over. Then if there's nothing different, I'll do as you described.

Like I said on the last thread, the AAR bench tested successfully. Open, closed, opened again. It was a 70 degree day when I tested it so it wasn't fully open to start.

I'm also still really wanting to hear from someone with a 1.8 L-Jet that gets a proper high idle on cold start... I could be chasing fiction.

[emerygt350]

Forceps don't give the best seal. Is it hard to reach the air cleaner hose? I have never had the honor of mucking around with a 1.8. I was also just thinking about 1.8 and leaks. That Aar leak is pretty big and the computer? Or something must compensate for that particular, momentary, leak. If it isn't there or not what it is expecting the outcome could be pretty unpredictable. Not like the 2.0 at all.

[StarBear]

All great stuff, mates! My flaps are on and working. Real thermos are available though pricey. I think I have the source (US) if needed; common to many VWs but there are two different versions.
35 F here this morning. Might try a very cold start and report. (IMG:style_emoticons/default/smile.gif)

[Van B]

I'm using the forceps to see if the engine wants a richer mixture on cold start. If the forceps result in a higher cold start rpm, then my working theory will be that the engine is too lean on cold start. If the engine struggles even more with forceps on, then the AAR is not providing enough air.

We'll see... It could also result in not a damn thing lol....

[StarBear]

Here's my Virgo Engineer testing this AM:
Tuneup 2 days ago. 49 degrees dwell; 7.5-8.0 BTDC (red mark on right side of V notch); spark plugs light gray coating - wire brushed and gap checked.
Set car out on driveway for 20 min @ 41F, 72% humidity; light wind, light clouds.
Deck lid open.
9:43 AM - cranked; 4-5 rumbles then steady at 1000 rpm (I tend to like my idle set a bit higher, and advance a tad more, than spec).
9:44 - 1100 rpm; steady
9:45 - 1100 rpm; steady
9:46 - 1000 rpm; steady
9:47 - 975 rpm; steady
9:48 - 1050 rpm; steady
A little idle dip at 3-5 min, then back up. (The AAR closing?)
5 mi drive to hardware store; ~ 15-20 min. Warm start @ 900 rpm; steady
7 mi drive home and around the block; ~ 15 min. Shut off. 45F. Full warm start @ 1000 rpm; steady.
Decel valve working fine (though still want to check it and adjust to 20 if needed)
Looks like all fine here in NJ!
(IMG:style_emoticons/default/driving.gif)
Van B: I like where you're going with this.... (IMG:style_emoticons/default/smile.gif)

[emerygt350]

It was 30F this morning. Took almost 8 minutes of cruising before the aar called it good. I assume it's the same part.

Fwiw I stole the bellows off a 1.7 van engine laying around in a friend's garage.... Seems to work well, my engine runs super cool though.

[Van B]

Here's my Virgo Engineer testing this AM:
Tuneup 2 days ago. 49 degrees dwell; 7.5-8.0 BTDC (red mark on right side of V notch); spark plugs light gray coating - wire brushed and gap checked.
Set car out on driveway for 20 min @ 41F, 72% humidity; light wind, light clouds.
Deck lid open.
9:43 AM - cranked; 4-5 rumbles then steady at 1000 rpm (I tend to like my idle set a bit higher, and advance a tad more, than spec).
9:44 - 1100 rpm; steady
9:45 - 1100 rpm; steady
9:46 - 1000 rpm; steady
9:47 - 975 rpm; steady
9:48 - 1050 rpm; steady
A little idle dip at 3-5 min, then back up. (The AAR closing?)
5 mi drive to hardware store; ~ 15-20 min. Warm start @ 900 rpm; steady
7 mi drive home and around the block; ~ 15 min. Shut off. 45F. Full warm start @ 1000 rpm; steady.
Decel valve working fine (though still want to check it and adjust to 20 if needed)
Looks like all fine here in NJ!
(IMG:style_emoticons/default/driving.gif)
Van B: I like where you're going with this.... (IMG:style_emoticons/default/smile.gif)

SB, what is your idle set at?
That's not much or a high idle but at least things were moving in the proper flow.
Thanks for the vote of confidence too lol!

[wonkipop]

It was 30F this morning. Took almost 8 minutes of cruising before the aar called it good. I assume it's the same part.

Fwiw I stole the bellows off a 1.7 van engine laying around in a friend's garage.... Seems to work well, my engine runs super cool though.

to me that sounds right for an AAR.
- would align with about how long my engine seems to be taking to get to something close to semi warmed up. the AAR is a different beast on the D jets.



thanks @StarBear for the weather report in NJ. (IMG:style_emoticons/default/beerchug.gif)
and countdown info.
does sound like the AAR on yours dips out a little bit early too - but is in better shape than mine and not in such a hurry.


pretty funny in the end.
whole thing is a kind of cuckoo clock bit of krautrock technology in a good sort of way. everything is timed but not necessarily very much is reactive.

[StarBear]

SB, what is your idle set at?
That's not much or a high idle but at least things were moving in the proper flow.
Thanks for the vote of confidence too lol!

Van B: After tune up I set idle screw at 1000 rpm. The car has always run best on cool dry weather.

[Van B]

Ok that’s good info. So, your cold start high idle is only about 100rpm higher. I would ignore the heat soak start you had while out running errands. That’s typical of any engine, IMO.

[wonkipop]

I'm using the forceps to see if the engine wants a richer mixture on cold start. If the forceps result in a higher cold start rpm, then my working theory will be that the engine is too lean on cold start. If the engine struggles even more with forceps on, then the AAR is not providing enough air.

We'll see... It could also result in not a damn thing lol....

i know what you are saying.

be interested to see what you find.

i'm kind of curious about the way everything is fine on mine for 2 minutes and then there is a problem for a short amount of time.

i'll be asking mechanic at workshop about it today to see what he thinks now i can describe accurately the sequence.

[wonkipop]

here is what mike (mechanic) had to say after i showed him the cold start description.

its either starving for air to burn the fuel its getting. AAV.

or its lean and does not have enough fuel. CHT.

as a starting point.

don't you love it. (IMG:style_emoticons/default/poke.gif)

but apparently it can be either.
there is a lot of fuel being splashed in there and a lot of it is condensing on cold surfaces so the air bit is important. car needs basically 10 times the amount of fuel at cold start up than when its warmed and at operating temp. i didn't realise it was that quantum!

he reminded me, it had been laid up for 15 years.
so you run it for a few months/year and see what faults develop if any.

in my car it could be that the CHT has started out ok and has progressively begun to "decay". have to retest.

or its the AAV. not opening correctly. either not opening enough at the start and not closing smoothly and timely. have to retest. he did say that 2-3 minutes was actually about right usually unless its really cold. then the thermo strip/spring is going to take longer to heat up from the colder engine block and ambient air and go a bit slower.

the thermo and cooling flaps were discussed. they could be playing into the hiccups speculated for either of other two - ie exaggerating them when its a bit colder here.
but they weren't really impacting a year ago he agreed. (i can test that with the car doing a cold start on the hoist by simply pulling on those flaps manually and easing them off, the cable is still there - which i might do when i get around to doing the other tests).

re emorygt350 idea of taking off a hose. yes. do that but....its a closed system. start the car with all hoses on. crack off a decel or aav line between aav and plenum carefully. you want to mimic an AAV valve if thats what you are after simulating. its a small ish aperture thats opening in the valve. so just crack it off like at one edge and control it.
one thing to remember is the AAV is in circuit with the AFM, so the flap might be being slightly opened with the AAV full open. i don't know that for sure, might have to dig around in the manual to see what it says.

as to what a cold start up is for a 1.8 - his view is - probably not that dramatic.
system would be trying to hold something like a normal idle from start up and not a lot more. maybe around the 1000 +/- rpm mark subsiding to 900 +/-.
and it would take anywhere from 2 minutes to 5 minutes depending on ambient.
but in australia he thought 2-3 minutes.

i'll wait until christmas to go further.

[Porschef]

I’m running Ljet on a 2056 with a 9550 cam

Cold start always requires a little bit of gas pedal, it doesn’t idle high and threatens to stall if i take my foot off. But cold start has improved greatly with the 123 distributor, and by the time I drive out of the neighborhood it is pretty much good

I think I do recall others having similar issues with anything other than stock engines

It runs fine otherwise

I hesitate to add a cable/rod activated idle increase device…

[emerygt350]

Yeah, definitely if you are going to pull off the plenum. If you just pull off at the air cleaner (pre AAV) then nothing changes to the system. You then put your thumb over the line and see what happens. Do you feel it sucking? Then the AAV is open. You can let it warm as normal and keep checking on whether it is still sucking. When the idle dips that is when you would suspect the AAV is closing and you should feel it stop sucking. If it is still sucking when the idle dips then you know it isn't associated with the AAV (or at least not directly).

Or you could be like me and just install a valve right before the air cleaner.

[wonkipop]

Yeah, definitely if you are going to pull off the plenum. If you just pull off at the air cleaner (pre AAV) then nothing changes to the system. You then put your thumb over the line and see what happens. Do you feel it sucking? Then the AAV is open. You can let it warm as normal and keep checking on whether it is still sucking. When the idle dips that is when you would suspect the AAV is closing and you should feel it stop sucking. If it is still sucking when the idle dips then you know it isn't associated with the AAV (or at least not directly).

Or you could be like me and just install a valve right before the air cleaner.

what i am getting at emery is that in an L jet you have the air flow meter flap up in the aircleaner where air enters. not so sure what D jet does, don't know anything much about D jet at all - which is what you have.

the flap is reading air flow which is also feeding info into the ECU for fuel.
if the aav in cold start is pulling in enough air that it is moving the flap thats going to be part of info controlling fuel flow maybe (as well as engine temp from CHT etc).

i was being cautious about the effect of pulling off a hose and the effect that has on more than just the AAV in an L jet engine. maybe not as simple as simply leaving off a hose.
see Van B's experience when he tried a start with a hose off.

that tap of yours is great as a test device i think.
it might be just the thing.
plumb that in where the AAV is and do a manual simulation of an AAV and timed.
that would keep the AFM in the equation.

[emerygt350]

Yes this is way different ljet to djet but the aar pulls clean air pre flap. Pulling the hose off the air cleaner will not mess up the flap in any way, that is why I am suggesting it rather than a controlled leak off the plenum. This way you can monitor the activity without disrupting our very sensitive ljet.

[Van B]

That's right wonki. Bypassing the AFM will throw off the whole fueling equation. It opens more variables than it eliminates. Popping the line to the AAR to check for air draw is feasible once the car is running. But I'm opting for pinching the short line in order to keep everything else accounted for. If pinching that line during cold start makes the condition worse, then to me it makes a strong case that the AAR is not meeting air flow requirements. Conversely, you could say that the engine is being over fueled, but given the objective of higher RPM than normal for engine warm up, such a statement doesn't make sense.

So, I start the car and then pinch the line:
1. RPM increases
2. RPM decreases
3. RPM remains the same

If #1 happens, then it's a lean condition I'm suffering from during warm up. If #2 happens, then it's a rich condition. If #3 happens, then the AAR is already closed.

What am I missing?

[Van B]

Emery, AFM is attached to the air filter housing. It's the sunset box on that diagram.

Subset* stupid autocorrect

[emerygt350]

Emery, AFM is attached to the air filter housing. It's the sunset box on that diagram.

Wow! That is nuts! I had looked at the layout in the Chilton's but it never hit me it was pre everything else. It seems insane to measure total air entering and then try to use a part of that total air to modify the afr. In fact it still doesn't make sense. Cake and eat it too. I must read....