[Gmecm] Tracker TBI Problems still

[Cowen]

Well, it failed AirCare again yesterday.  I am getting
the CO a little lower, but it's still high.  It's
allowed about 12.5 g/km, but it's reading about 14.25
g/km.  All other emissions tested are good.

My mom has the identical car (even color!), and it
passed AirCare on Dec 19th no problem.  So, I've got a
source of known good parts!  Here's what I've done:

-Cleaned/tested EGR
-Cleaned EGR vacuum modulator, then swapped it
-Cleaned/tested PCV
-Cleaned IAT and ECT sensors to ensure connectivity
-Cleaned and greased all engine grounds (4)
-Disassembled and Cleaned Throttle body, blew out all
passages w air, new gaskets
-Set valve lash
-Confirmed good, even compression
-Tried to inspect injector spray pattern w strobe, pod
obstructs view, but no large drops - seems to be a
mist
-Checked Fuel return line - clear of obstruction
-Compared Fuel Press Reg with mom's - couldn't make
either do anything, so at least they're the same.
-Checked purge canister - not flooded w gas
-Checked all vacuum hoses - no leaks, no obstructions
-New plugs, gapped to 0.028"
-Checked base timing.  Strange, I shorted the check
connector as per the VECI, but couldn't affect the
timing.  Have I lost ECM control of timing?  How??
-Swapped cap, wires, rotor, and distributor
-Swapped coil and ignitor
-Swapped TPS
-Swapped O2
-Swapped MAP and MAP line w filter
-Confirmed MAP port on manifold is clean
-Replaced suspect capacitors in ECM
-Swapped ECMs, although I didn't actually run it
through an AirCare test with swapped ECM, because it
didn't feel like it ran any different with Mom's.

Symptoms: Beginning quite abruptly in late August,
abysmal mileage, hesistation/light missing on light
acceleration.  Oh, and has failed Aircare for the same
reason 3 times since Nov 25th!

Strangely enough, I did a ton of work in one day,
including redoing the TB, and it ran PERFECTLY for
about a week!

It runs well otherwise, uses little oil, and has
plenty of power.  What am I missing??  Why does it run
so rich?  

Thanks for any suggestions!

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