Below is my canned post about the V/C ignition and how tha vacuum can be plugged to reduce NOx emissions with little or no effect on performance.

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You have the Volvo/Chrysler ignition used on 240s from mid '81 thru 1988. It's been found that the V/C Ignition can contribute to High NOx, and that plugging the vacuum line to the ICU can reduce NOx levels, with little or no effect on normal operation. Note that this is NOT a guaranteed fix, but worth a try if your other numbers (and cat) are good.

This is my canned post on the subject. It might work for you as it has for several others, especially with a new cat. This isn't my own theory -- I just happened to find it on a 'net search in 2004. For a technical description, see the original post here, and the first success story here.

Other positive responses are posted in this thread and this one,
and one more here.
Yet another one .
And another on 2/04/06.
Here's the latest, from 3/12/07.
And 1/29/08 Here .
Also 7-09-08 Here.
Another reported on 3-26-09
--
Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

Your original post you said you were fighting high gas mileage. Interesting how you meant that?

I beleive that the vacuum connection is for the module to have a sense for load of the engine. Therefore it can adjust the timing for the change in fuel charge under load. It's sort of like a knock sensor backup if you will.

It might be safe to say that the module altogether was a hybrid unit. Before the better/consoldated ECU's came in to play to address future emissions.

I sincerely doubt that it makes any difference in a smog unless a dynamometer is use in the testing or some one was really checking things closely.

I like things stock, don't you? The reason is: If a manufacturer actually spends the money to put someting on. It must be needed to do something for the better, I would think. It may be done on the cheap side to get by, but it must have needed it.

Colors of paint are optional. Their needed for eye appeal which equals sales appeal. The paint gets put on as thin as possible too!

We will see if this post gives any "bearings" on the direction of your decision.

Phil