On my 1.7, if I disconnect the advance side of the vacuum advance, and pull a vacuum on it, the idle increases... but over about 2 seconds, the vacuum leaks away and the idle slows down again. That's bad, right? Anyone know if the 1.8 vac advance is the same? I'm trying to chase down an abnormally slow idle.

Yes. Sounds like you have a pinhole leak in your vacuum canister. Unfortunately, I don't know if these are still available new. You might have to hunt for a non-leaky used part.

Doubtful that this is causing any problem except for a very slight (as in unnoticible) deterioration in acceleration. A very small leak will not affect it much. Later d-jet cars had the vacuum advance completely disconnected. Of course, no leak is better, but if you are looking for a solution to a problem you are having - keep looking. This isn't it. If your idle speed is low: 1. check timing. 2. increase speed using idle speed bleed screw.

Demick

Demick is right, a leaky vac advance isn't going to affect your idle. At idle on the D-Jet 1.7's and 2.0's, with the throttle closed the vacuum retard port is exposed to manifold vacuum and the timing is retarded, for improved emissions. When at part-load with low throttle angles, the vacuum advance port is exposed to some degree of manifold vacuum, and the timing is advanced. The operation of the advance mechanism is dominant over the retard (i.e. if both ports are exposed to vac, the advance port controls the timing response). The reason for the timing advance at part load is that due to the fairly high manifold vacuum, the cylinder charge is of low density, and the flame front takes longer to propagate across it, hence, the need for advanced timing. Primary benefits are slightly better throttle response and lower emissions.

If you are really wanting to replace your VAC advance there
is new one for sale on ebay right now.

http://cgi.ebay.com/ebaymotors/ws/eBayISAP...bayphotohosting