OK i have read many many posts on this topic so i am trying to put all this into one post and see if a) i finally have it figured out a b) answer some last questions.

This is for an '81 US L-Jetronic car.

Below is a picture of the throttle, the shop manual labels 3 ports

Port 1: (front of throttle) distributor retard
Port 2: (rear of throttle, driver's side) decel valve, pressure damper, fuel pressure regulators
Port 3: (rear of throttle, passenger side) distributor advance, temp switch for carbon canister shut off valve



From studying the throttle, I think the following is true:

Port 1A provides manifold vacuum, with the butterfly passing over it with throttle just beyond idle

Port 1B provides manifold vacuum, with the butterfly passing over it with slightly more throttle than 1A

Port 2 provides manifold vacuum, larger diameter than 1A or 1B and way above the butterfly

Port 3 provides Ported vacuum, open to manifold just after idle.

Now the questions:
- Which Port 1 does the distributor retard attach to?
- What's the difference between the timing of port 1A and 1B?
- What (if anything) connects to the "unused" port 1?
- where does the diverter valve (or blowoff switching valve) connect to? I can't find a diagram anywhere relevant to '81 that indicates where it goes.

After reading up on it, I would tend to think it wants ported vacuum so you are not pumping extra air into the cat at idle. Does this make any sense?

If i get confirmation to these things and answers I'll edit the post so everyone will have the answers in one place.

Thanks!

 

found this reference in the '81 service information bulletin. would seem to indicate that the diverter valve goes to port 1B, which is just above the butterfly on the manifold side

 

Thanks for posting this, it should help out quite a few people.

 

Good timing on this post.

I'm doing some research on the emissions system on my '87 s4. I would like to remove the air pump when I do the timing belt (Porktensioner) and have found all the helpful posts. I've often found you can remove most of the emissions equipment/tubes in a car without harming anything, but I want to be sure.

 

well i just found out my diverter valve is broken, but is stuck in the direction that routes the air to the air filter, so i think for now i can leave it as is, just plugging the vacuum line...looks like it will be a bear to get out anyway.

Started it up after all that manifold work, and now looks like my decel valve has gone bad.(I had checked it with a mightyvac when i took it off) I have that "wandering idle" i've heard described here ..it gradually increases rpms, then rapidly drops off, then gradually increases again