Van wants to die when throttle released (when cold)

[Gauche1968]

So, the van has a normal idle upon start, but if I rev the throttle and release it wants to die. It does not return to a normal idle speed. This seems to be an issue only when cold. At operating temps it seems OK. This is a relatively new symptom that has emerged after a period of excellent running.

I know, use the Bentley and run the tests, but any suggestions on where to start?

Thanks!
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1984 Vanagon GL
1984 Vanagon Westy

[jlrftype7]

Check for a vacuum leak that might be sealing up once the engine, and seal or gasket, warms up. If you don't have a Smoke Tester, or don't yet want to look up how to make or buy one, then use the old fall back technique of Spraying Carb Cleaner in tiny bursts around all known hoses, and connection points of the Intake System.
Another sneaky one that's gotten me with dying out on our 1.9 is a crack, on the bottom, of the hose going from the Crankcase Breather Tower to the Intake Boot. I've had a split on the bottom of that hose twice, probably from oil residue attacking the hose over time from the inside.

Intake Boots develop cracks as well. It's easy enough to pull yours off and carefully inspect it.
Don't overlook the little plastic tees ,and small hoses under the Intake Boot, at the Aux Air Valve area and manifold.

Last thing, use a Multi-Meter and check your Throttle Switch for a good idle switch signal. Don't rely on just hearing the 'CLICK' from it as you open and close the throttle by hand. Get a resistance check to see if you have a good signal with a cold engine in case your switch contacts are going goofy when cold, but start working all the time once the engine heat gets to them.
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'68 Westy- my first VW and vehicle/Bus- long gone.- sold it to a traveling Swiss couple....
'67 Type 3 Fastback, my 2nd car- gone
'69 Semi-Auto Stick Shift Beetle-gone
2017 MINI Coopers, our current DDs
‘84 Tin Top - Hilga....Auto

[Howesight]

I suggest that you start by checking the throttle switch and the Auxillary Air Regulator (AAR). Both of these are described and diagnostics are explained in the Digitjet Pro Training Manual. You can find it here:


https://www.thesamba.com/vw/archives/manuals/vanag...ystems.pdf

The AAR disk can get sticky and stick close to the closed position. You can clean up the disk with BrakeKleen or similar product and compressed air.

Do you notice any indication that your engine is running unusually rich when this problem occurs? If so, then it may help to check both the coolant temperature sensor and its wiring to see whether the resistance signal that the ECU is receiving during warm up is a false signal.
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'86 Syncro Westy SVX

[4Gears4Tires]

[Gauche1968]

Thanks for the suggestions. I will report back!
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1984 Vanagon GL
1984 Vanagon Westy

[Gauche1968]

Reporting back: Temp II tests perfectly when cold. I have about .5 ohm resistance in the wiring from the throttle switches. I unplugged the connectors from the idle stabilizer unit, plugged them together and started it up. The idle was extremely low and eventually stalled out after about 3 minutes. It seems like it is choking out. Next, I will check timing (assuming I can get it to idle long enough), test fuel pressure and look for a leak down after shut off. I do not find any obvious source of a vacuum leak. I will remove the spark plugs and check for gas fouling. Any other suggestions? Thanks!
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1984 Vanagon GL
1984 Vanagon Westy

[hdenter]

Did you check/clean the Aux Air Valve? On an '84 that doesn't idle well when cold, that's my first check. If it's stuck closed you will have a crappy low idle till it warms up. If it is stuck open, you cold idle will be fine and once it is warmed up your idle will surge up and down like a big vacuum leak. See if your is stuck closed...

Hans
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'79 triple white convertible bug
'84 sunroof vanagon
'85 weekender

[jlrftype7]

Also, since you have a meter, check for infinite resistance between the center wire on the O2 sensor wire, body harness side, with your O2 sensor disconnected.
You're probably NOT experiencing this, but it's so easy to check with your Meter, and you learn something about your Fuel System as well.

Put your Meter on Ohms, one probe/wire attached to the flat pin of the O2 sensor body harness side, and the black meter wire on a really good ground in the engine compartment.

We are checking to make sure no shield wire connection between the center, inner most signal wire that is connected to the O2 sensor, and the braided shield wire you can't easily see, that's wrapped around the inner wire to shield it from inductive signals or interference. So, a Coax cable in other words.
They can't make a connection, if they do, the ECU signal is grounded out and your engine runs rich. Can start as an intermittent issue , so it's one easy thing to check with your meter. So, ideally you see Open Circuit or something like a million ohms on your meter reading when checking.
There are threads here on Samba about the last inch or so of the braided wire strands getting work hardened, and piercing the insulation of the inner signal wire, making that stupid short to ground that we don't want.
See the picture below, you can just see the braided section surrounding the inner signal wire, damn strands poke inward and you're screwed until you trim back a small amount of wire in the braided section and stop the short/connection

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'68 Westy- my first VW and vehicle/Bus- long gone.- sold it to a traveling Swiss couple....
'67 Type 3 Fastback, my 2nd car- gone
'69 Semi-Auto Stick Shift Beetle-gone
2017 MINI Coopers, our current DDs
‘84 Tin Top - Hilga....Auto

[Gauche1968]

[jlrftype7]

[Gauche1968]

So, I found today that the timing will not set. It is jumping around even with the idle stabilizer module disconnected. Trying to advance the timing, I can keep it from stalling, but the engine is shaking and the timing is not staying set. So, this may be ig ition related. I am only able to work on it for an half hour here or there right now.
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1984 Vanagon GL
1984 Vanagon Westy

[DanHoug]

[jlrftype7]

[Gauche1968]

[Gauche1968]

[dabaron]

i would use the troubleshooting steps in the ProTraining Manual.

http://keg.s3.amazonaws.com/westy/digijet_protraining.pdf.zip
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1991 Vanagon GL Camper
i had no idea i wanted to be a mechanic