Rough idle when cold

[Nickel_Nackel]

I have been dealing with rough idle when the van initially starts up. After it gets warm the problem seems to go away. The rpms are dropping in a surging sort of way and it never really dies, stays about 400rpm then jumps to 950 and drops back down.

This problem happens when I bypassed the Digital Idle Stabilizer, but when I plug in the DIS it runs smooth from the start but will randomly die. I think there is a underlying issue that the DIS is fighting until its just too much and dies.

also the van will not start up if it dies with the DIS plugged in, it will only crank until I bypass the DIS.

Is this a timing issue? I have adjusted the timing to spec and it runs amazing once its warm. After I let it sit and start it back up the same problem occurs.

I have replaced my distributor minus the retard hose because the breather attachment didn't have one. But I am told this is fine.

I have replace and examined every vacuum hose I see, replace the TB gasket as well. (sprayed carb cleaner and cant find a leak anywhere)

I have a gap in my TB but its not major compared to some I have seen on past threads.

I have also pulled my Air Aux Regulator valve out a tested it and it works fine.

I have replaced everything else that I can think of and this problem is still there.

I did notice when I pulled my oil fill cap off the van starts to drop rpm and surge like it does even when its warmed up. I don't know what that could mean.

Thank you!
-nick
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1985 1.9L Potato

[Wildthings]

The worn Digijet throttle body will allow the idle speed to exceed the fuel cutoff speed and you will get severe surging, this is worse when the vacuum retard is not functional. Try removing the wires form the Throttle Position Switch and see what that does. If too much idle air is your problem then closing off the hole in the throttle plate can help. Finding an fixing all vacuum leaks is important here as well.

What did you set your timing to? 28° BTDC @3800+ rpms with the hose(s) removed and plugged works best IMO.

[Nickel_Nackel]

I am wondering now if I still have not set my timing correctly.

I have two marks, one on the U shaped groove and one 2 inches to the right of that groove. I then set my timing light to 0 and rev the engine to 3500 and let the second mark line up with the crankcase seam. tighten bolt.

Is this correct?

does 28 degrees BTDC @3800+ mean I can just set the timing light to 28 and use the U shaped groove (lining up with seam) while running the van at 3800 rpms?

right?

Do I need to factory set my idle adjustment screw? I feel like I'm missing something because that screw will put me out of wack once I start adjusting it.

I pulled the two wires from the throttle position switch and instead of surging and staying running it just surged a few times and died.

I might pop my old vacuum diaphragm back in so I will have the vacuum retard and see what it does.
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1985 1.9L Potato

[4Gears4Tires]

That's right, if your light is adjustable, set it to 28 degrees and use the u shaped groove. Don't touch the idle adjustment screw until after timing is set.
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'87 Syncro
Ferric Oxyhydroxide Superleggera Edition

[Wildthings]

I think your engine dying is due to a bad DIS. I would just leave it bypassed for now.

[Nickel_Nackel]

[Nickel_Nackel]

[Wildthings]

[Nickel_Nackel]

oh shoot, I thought you meant distributor. So when I have my Digital Idle stabilizer connected the van runs great and idles perfectly. But it will randomly die. Then crank no start.

Once I bypass the DIS it will fire up and surge at idle. This is why I think there is an underlying issue rather than just the DIS is bad. The Dis could be bad but even if I bypass it I still need to get the van running better than it is because I cant find a Dis anywhere online.

when I set the timing do I only pull out the two hoses that are on both sides of the TB? and plug em? are there other hoses im missing? FPR?
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1985 1.9L Potato

[Wildthings]

A bad DIS can cause an intermittent spark or no spark condition. Do you have a spark when the engine dies and doesn't want to start?

Assuming you have a double vacuum distributor you want to disconnect the two hoses that go to it and plug them off when setting the timing at full mechanical advance. You need to remove just these two hose and can leave any other vacuum hoses on the engine connected.

You also want to verify that the retard can (the nipple pointing towards the distributor) holds vacuum, as they very often have failed. If yours will not hold vacuum you want to leave the hose off and plugged as it is just another vacuum leak at this point.

[Nickel_Nackel]

So yes the DIS does prevent me from starting it once it dies (bypassing it get the van started) I think I remember testing the spark with the DIS connected and I did get a spark. I will check again.

If the Dis is the culprit for dying randomly and not starting back up I still have a issue, right? because I should be able to run the van without the DIS.

I have a single and a double vacuum distributer diaphragms but currently I am running the single because that was the one that came with the Distributor. I put my mouth to both and they all hold suction.

Thanks for the help, Ill test spark and set timing and see where I'm at
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1985 1.9L Potato

[Wildthings]

Anytime a fuel injected engine is running rough or has less than normal power I like to add FI cleaner to the tank and see if that will help.

[Nickel_Nackel]

okay so I set the timing to 28 degrees @3800 and the idle was around 1500rpms but once I began to adjust the screw to get it around 950 I looked at my timing again and the U notch is no longer aligned with the crankcase seam @3800rpm.

Is this fine? I feel like something is off? should I be adjusting the crew as I am setting the timing so the adjusting of the screw is very minimum? I hope that question makes sense
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1985 1.9L Potato

[Nickel_Nackel]

I noticed this only happens when I put the distributor vacuum advance hose back on. so I left it off and adjusted the idle screw and the timing seems to stay where it is all in. so far so good. runs great but it is warmed up. so I'm letting it sit and will try to cold start it and see what happens
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1985 1.9L Potato

[Nickel_Nackel]

can I cover the hole in the butterfly with duct tape to see of there is a change? or is that bad idea?
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1985 1.9L Potato

[Wildthings]

[oceanair]

IF you are setting the timing at high RPM for full advance, leave everything plugged in, including all of the vacuum lines. Open the throttle until you see full advance and the mark you made 2 inches from the U on the pulley should be at the seam of the case. Done. If not adjust with the distributor. Keep it simple.

Than adjust the idle screw. If you have a leak at the throttle body, don't duct tape it, replace it.
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84 Vanagon Pop Top Conversion from Tin Top, 1970 Ghia - all sweet rides! Love em!
Previous: Green 72 Tin Top, White 72 Westy, Blue 64 Beetle, Yellow 71 Squareback, 2014 Jetta TDI Wagon - wish I could have them all back!

[Wildthings]

[Nickel_Nackel]

I plugged the butterfly hole with a 3mm screw. No change in idle. I am wondering if it could be the carbon wearing down at the AFM? I can always keep the van running as long as I open the throttle. So I am thinking there is some sort of delay in the AFM not giving the throttle enough air?

before I get too ahead of myself would it be wise to adjust the carbon track by just loosening those three screws?
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1985 1.9L Potato

[Wildthings]

If you test the AFM according to the Bentley and it passes the test giving nice smooth readings you don't want to do anything to it.