[s-cars] Emissions fun

[JAM]

Not to be captain obvious but when was the last time you replaced the O2
sensor?  Generally, it will go bad and the ECU doesn't pick it up and  not
throw any codes.  My gut tells me that if you have a vacuum leak, you'd run
lean because you have extra air getting in beyond the MAF but that's just a
hunch.
Good luck!
Jason
Boone, NC
'95 S6
'83 urq
'90 CQ
'01 A4 1.8tq



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? 

Sent from my iPad
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