The car is a 2001 A4 1.8T fwd, automatic. Miles: 153k

After driving the car for a few months while showing the O2 sensor code, I finally decided to change it out. Simple enough, huh?

Disconnected negative battery cable.
Disconnected O2 sensor cable.
Unscrewed O2 sensor.
Assembly, as they say, is the reverse of removal.

Hooked battery back up and cranked car.

Runs like total crap. Won't idle. Won't drive.

Put old O2 sensor back in. No dice. Same thing.

Put new O2 sensor BACK in. Still crap.

The symptoms, as best I can describe them are: car doesn't seem to take throttle sometimes. when it does, I can get it to hover at around 2500 rpms, but when I try to go higher it stalls out. Quick throttle pulses stall at around 3k rpms.

I was hoping it was bad gas (I had just filled up prior to the O2 work). Drained the tank and went back with new. No luck.

Next I was hoping it was a fuel filter. No luck after replacing.

Next I checked the fuel pressure. Plumbed a gauge into the pressure line feeding the fuel rail under the hood. Solid at 55-60 psi.

Checked the air hoses leading to the intake manifold. No cracks.

Had the wife actuate the throttle while the air supply hose was off. butterfly valve seems to follow throttle position appropriately.

I'm out of guesses. Before I shoot this thing in the head, any ideas?

I should also mention that I took the car to a reputable shop. They spent four hours on it, replaced the spark plugs with some that are apparently made of unobtanium ($70 worth!), and did a "seafoam treatment". Charged me $500 and I left with a bit of a limp. Anyway, they showed me the old plugs and they were sure enough carboned up. This should have been my first clue that fuel delivery wasn't the problem, but I wanted to check it anyway, just for my own (in)sanity.

While I'm at it, I'll give some more hints related to the way it drives currently. Seems to idle pretty rough. When in gear, I can feather the throttle and find a little sweet spot where I get some response for a moment. When it starts to go dead, I floor it and start feathering again. Lurch forward stall lurch stall. The cat is getting sure enough hot. Smoking and stinking when I shut it off. I'm thinking cat, but I'm not spending that kind of money, not knowing for sure. And the gurus at the shop were non-committal on whether they thought the converter was the problem.

Again, any ideas?

Thanks,

Jason

'01 A4
'07 Jetta 2.5
'86 325es

 

Engine:
16684, 16688, 16497, 16514, 16686, 17511, 16687, 16685m 17887, 17524, 17769, 17776

Transmission:
18265

I'm trying to figure out how to clear the codes with my scanner and I'll see which ones come back.

Thanks,
Jason

 

Once codes are cleared, these come back pretty quickly:
Engine:
17887 (within a minute)
16514 (about 5 minutes)

A/T:
None (yet)

I can get the RPMs to about 3500 without any problem. Beyond that it stalls out. Flattening the accelerator gets a further stall until I let up, and it will rev up to 4k very momentarily then drop back down....

 

Another code update:
Engine:
17887 (within a minute)
16514 (about 5 minutes)
16684 (~15 minutes, after a short 1 mile drive through the 'hood)
16688 (showed up with 16684)

A/T:
Still None (yet)