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Tue Jun 25, 2024 1:06 pm

I recently bought a 85 vanagon and on my drive home I ran into a problem. Once the van got up to a decent temp the engine idles out of control in neutral. At speed in 4 gear it was running fine but any time I put in the clutch pedal it would dam near redline. Any ideas where to start?

Tue Jun 25, 2024 2:24 pm

Is the Throttle hanging up at all? Or the accelerator/throttle cable.
Since the VW is 'new' to you, it's worth checking the throttle switch for the contacts to be set correctly while the engine is at idle, or the throttle is closed.
Hearing a 'click' from the throttle /switch right as you open it, or close it,[ engine off], is a first step, but it's best to measure the switch resistance to make sure the Engine ECU is seeing the correct signal at idle or just off idle.

Your issue seems like a binding throttle though[ they get worn in the bore, the throttle plate becomes an issue, as does the shaft]
Let us know how the throttle feels by hand -ENGINE OFF- does it seem hard to manually open and close as you try it?

Tue Jun 25, 2024 5:08 pm

When it does this, open the hatch and turn in the idle screw all the way in.

Sometimes it takes a throttle blip before you’ll see idle come down as it should when turning in the idle screw.

If the screw’s in all the way, it means you’re still getting air, from a hanging throttle or wear like the above post, or from air getting in elsewhere. A smoke test would show where there’s leaks in the vacuum system.

Another trick is spraying carb cleaner right at the little hoses connecting the manifold pipes to the center plenum, those are notorious for failure and show their failure by raising idle speed briefly when sprayed.

There’s many other suspects beyond the aforementioned. All revolve around excess air getting in: the intake boot loose or leaking, a crack in anything connected to vacuum, the hoses themselves, a cracked manifold (unlikely), loose clamps, etc.