Pulsing at idle/lower RPMs

[JimiD]

I've got a weird issue with my 1984 1.9 Vanagon.

When the engine gets up to temperature, it will rev the RPMs in a pulsing manner both at idle and when I'm slowing down from a driving speed.

It is an automatic transmission, and it doesn't have this issue if I am stationary but still in gear (such as at a stoplight), and it doesn't occur when I give the van any gas (like when driving/revving the engine at idle). So the engine having a load on it directly affects this issue.

Things to note,
I have replaced the fuel filter, (I'll be checking this and the fuel tomorrow, just in case there is water or something in there)
I replaced the temp 2 sensor.
I replaced the oxygen sensor, but still, have an oxygen sensor light on on the instrument cluster for some reason.
I've replaced the ignition coil, distributor cap, rotor, and sparkplugs/wires.
I also checked for a vacuum leak, but couldn't find any. (I'll probably double check this though)
I also tried a different airflow meter, and the same issue occurs with that one.
The engine also runs pretty rich, and when it's doing the pulsing thing the exhaust smells pretty strongly like there's probably some unburnt fuel in it.


I just checked/adjusted the timing a little, but didn't want to change it too much.
As I retarded the timing, the pulsing seemed to mellow out a bit, but not completely. When I got to the point where the pulsing seemed to mostly go away, it no longer had the correct 35 degrees of advance when "all in", so I adjusted it to what I think *should* be correct timing, and the issue is still present.

I'm having a really hard time figuring out what this issue can be, has anyone had any similar issues?
Could this be an issue with my O2 sensor giving bad feedback to the ECU?
Could it be the fuel injectors?
Could it just be the timing pulleys on my engine aren't correctly lined up, and it needs slightly less advance?

Any insight on this would be greatly appreciated!

Thank you all,
Jimi

[MarkWard]

Are the throttle switches connected and working? There is also an adjustment. I say switches because I recall the digijet had one or two depending on generation. The digijet has a digital idle stabilizer mounted next to the coil. You need to disconnect both leads and plug them together when adjusting timing. It controls idle speed by small timing adjustments.
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[markswagen]

the OXS light in the dash,
follow the speedometer cable from the wheel to the sway bar, you will find a box the cable goes in one side and out the other to the dash, there's a button on there, push the button, the OSX light should go out, and stay out, for 10k maybe 15k miles, i don't know, i've never bothered to find out.
it's like a service light on a modern car.
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markswagen {mobile mechanic} san diego area all early VW's cared for.

619 201 0310

[JimiD]

[JimiD]

[MarkWard]

Nothing wrong with timing for total advance. But what you should do is watch the timing mark while the engine is idling. It's likely moving around as it should, but you might see the movement corelate to the surge.

Bypassing it takes it out of the equation completely. You might find the idle improves with it bypassed.

The digijet should have an auxilary air regulator for giving you a faster idle during warm up. It should also have at least on solenoid valve on the firewall by the air cleaner for raising the idle when power steering pressure is at limit. With AC, it will have an identical valve mounted next to it connected to the AC compressor circuit.
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[JimiD]

Hello everyone,

Sorry for the delayed update.

I'm realizing now that the reason it does it after it gets up to temp is because the AUX air is working properly and giving it extra RPMs. But once it gets up to temp, it closes off and the issue starts becoming noticeable.

I checked the timing at idle while the engine was doing the pulsing thing, and like MarkWard stated, the pulsing seems to be corelated to timing mark jumping around. But the issue didn't seem to improve when I bypassed the idle stabilizer either.

On another note, I was able to get my OXS light to go off thanks to Markswagen's insight on that!

I also checked the fuel filter, and some of the fuel that was in the fuel tank, and there was a negligible amount of water in the fuel (1/4 teaspoon in ~1.5 liters of fuel).

I'm going to be double checking for vacuum leaks and making sure all my electrical connections are good. Can anyone thing of anything else I should think about testing?

Thank you all,

-Jimi

[MarkWard]

There should be zero water. Common water entry points are the fuel tank expansion tanks located in both front fenders. There is a valve on top with a large grommet that fails over time. Water and dirt are thrown up there by the tires where gravity takes over and funnels it back into the fuel tank.

I no longer reseal or replace fuel tanks without dropping both expansion tanks.
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[JimiD]

[MarkWard]

Your engine should have a vacuum advance diaphragm on the distributor. It should have 2 fittings. One is connected to intake vacuum and the other gets vacuum at throttle. These units do fail and leak vacuum. Have you tested them? The inner fitting pulls timing retard and the outer nipple pulls timing advance.
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[oceanair]

[MarkWard]

I clean the original tanks with soap and water. Reinstall with new grommets.
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[JimiD]

[Howesight]

You test them with your vacuum pump with a gauge. First ensure that your vacuum pump with gauge is attached to the vacuum canister with a properly-sealing hose. Pump to vacuum. Observe the gauge. It should either hold steady or leak down VERY slowly. The factory vacuum hose can leak a bit, so check that it is not a leaker. If a distributor vacuum actuator is leaking when you test it, you will likely hear a hiss.
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'86 Syncro Westy SVX

[djkeev]

Out of curiosity, while your erratic idle is occurring what happens if you remove the oil fill cap? Even just loosen it to break the seal?
Put it back on.......
Now....

What happens if you pinch close the hose from the engine vent tower to the intake?

Dave
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http://www.thesamba.com/vw/forum/viewtopic.php?t=392473

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http://www.thesamba.com/vw/forum/viewtopic.php?p=6315537#6315537

Beetle
https://www.thesamba.com/vw/forum/viewtopic.php?t=482968&highlight=74+super+vert

[JimiD]

[JimiD]

[16CVs]

Sounds like classic dirty grounds to me. My 1.9 did this to me one time, it was running rich as hell and I tried the throwing parts thing at it and it ran really well after I cleaned the grounds.

Stacy
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1987 Syncro Westfalia Triple knob (bastard)
1989 Syncro Tristar Triple knob "Swedish"
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Samba member # 14980
Call anytime number 650 722 4914 .
Keep Your van running and upkept tastefully for the love of the hobby.
Don't let your van end up in an "abortions" thread.

[eeebee]

Bad grounds or connections is a possibility. It probably doesn't happen before it comes to temp because it is running in open loop where it is ignoring the sensor inputs. There is a fuel injection trouble shooting manual i've seen which is a big help.
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Eric

1987 Vanagon Wolfsburg Special Edition
GoWesty 2.3

Democracy is the recurrent suspicion that more than half of the people are right more than half of the time.

[vandam]

https://www.thesamba.com/vw/forum/viewtopic.php?t=570224&highlight=

search air flow jimmy rig if this link doesn't work, my 1984 Vanagon did the same thing and then I adjusted the circuit board so the wiper hit fresh carbon track, fixed my issue, and might be worth looking at. You can see in the photo that it had worn a spot into the board. Good luck

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84 GL, 2.1 rebuilt