Cleaned the injectors, now very rough idle

[SlowLane]

Question for the group: Why would the decel valve, when connected to the (plenum) vacuum, make the idle go up. It will also kill the engine if the airflow from the decel valve to sboot is cutoff while it is hooked to vacuum (and idling fast). When not hooked up to vacuum the decel valve has no impact. I am trying to understand the theory behind the decel valve. (it is germain to Kubelwagon's issue here so this is not a threadjack).

The decel valve is pretty simple: it just opens up a passageway around the throttle body when the manifold vacuum exceeds its preset opening level. Generally speaking, that level is high enough to only to be expected on throttle overrun (like when descending a hill or lifting your foot off the throttle at speed.), but higher than you would expect at other conditions like idle.

It's also pretty easy to check with a MityVac. Just connect the MityVac up to the decel valve signal port (the tiny one), apply mouth suction to the port that normally connects to the plenum (it shoud be closed at this point), then start pumping the MityVac until the valve opens and you start sucking air. Stop sucking immediately. Note the reading on the MityVac. Repeat until you get a representative sample. If it doesn't present an obstruction to mouth vacuum before pumping the MityVac, then the valve is hosed.

I have two decel valves that I've performed this test on. The one that came with my van (an '81 Canadian model) opens at 20-22" Hg. The other one is from an '80 CA-spec van and opened at about 17" Hg. This could either mean that the CA-spec one is fubar, or that the typically lower idle vacuum on a CA-spec model allowed VW to use a lower trigger vacuum on those decel valves. If that's the case, then one must be careful to not go swapping decel valves willy-nilly, as mounting a CA-spec one on a Federal engine could cause it to open at idle, for instance.

It would be a very good idea to have a vacuum gauge connected to your intake manifold while you're troubleshooting the decel valve. Otherwise you're just guessing. Even nicer to have one in the cockpit to watch the engine's reactions to various driving conditions.

FWIW, the part number on my original decel valve is 071-133-551. The one from the CA-spec van is 071-133-551A

[dingo]

Even nicer to have one in the cockpit to watch the engine's reactions to various driving conditions.

that sounds like a great idea...but does the engine get uncomfortable with 14ft of vac hose running up to the cockpit..or does it not care ?

[SlowLane]

Mine doesn't seem to care. It's static vacuum. Basically it increases the volume of the plenum by a tiny amount.
You do need to be careful running the hose to make sure it isn't exposed to sharp edges which would saw through it, but it would be pretty evident if that happened anyways.