[s-cars] Emissions fun

[tedebearp at yahoo.com]

My '92 S4 isn't passing the idle portion of the smog test due to high HC.  It does fine in other areas.  I've noticed the engine idles a little roughly and the exhaust smells rich.  No codes.  I also noticed the AC won't stay in recirculate mode reliably.  Sometimes it switches back to fresh air as soon as I push the recirculate button.  I'm looking for a vacuum leak.  I already replaced all of the vacuum hoses for the ECU and FPR a few years ago.  I disconnected the hose from the intake manifold and tested it with a vacuum pump.  No leaks there.  My next area of testing is the vacuum hose right below that one, which goes to the plenum and all the HVAC solenoids.  Unfortunately my vacuum pump chose to crap out at that point, so testing will have to wait until I get a new one.  In the meantime, those vacuum hoses look original, so I'm going to replace them.  Anybody know the size?

Also, where is the vacuum solenoid for the recirculate flap?  Is there a good vacuum hose diagram in the Bentley manual?  I didn't see it.  I'd like to find a picture that shows me where the hoses and solenoids are in the car.  The hose from the intake manifold attaches to a plastic tee.  One hose from the tee goes into the plenum where it ends in what appears to be a check valve in a large canister.  The other hose from the tee is a fabric covered hose that attaches to a thin plastic line that runs down and disappears into a grommet in the firewall.  Anybody know what this one is for? 

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