1999 C4 3.4, need a sanity check before parts arrive.

Symptoms: with MAF connected, engine starts and dies within ~1-2 seconds, throttle doesn't save it, and it revs hesitantly like it's choking. With MAF unplugged it runs: slight misfire when cold, barely noticeable once warmed up, and I even drove it about a kilometer. AC load nearly kills it even without MAF. No fuel smell from exhaust. Cold start, so it dies long before O2 sensors come into play.

What I've tested so far:

1. Swapped in a known-good MAF from my other 996 that runs perfectly. No change. So it's not the sensor itself.
2. Cleaned MAF connector contacts. No change.
3. Spraying intake/carb cleaner into the MAF opening smooths it right out, misfire calms down. So it's running lean.
4. Oil filler cap on/off makes zero difference either way.
5. Fuel level: tank filled to the top, no change. The in-tank transfer hose (which failed on this car before with similar symptoms) checked and it's like new.
6. Battery is brand new, was replaced during this.
7. Fresh fuel filter is going in, and a new oil filler tube is on order: mine has an old crack in the corrugated section, currently taped up. My main suspect for an unmetered air leak into the crankcase.

Advantage: I have a second identical 996 that runs perfectly, so I can pull literally any part off it (coils, sensors, whatever) and swap it in for testing.

Plan: smoke test first (machine arrives tomorrow), then oil filler tube, then NGK plugs. Coils are cheap aftermarket, I have OEM ones to swap for testing if it still acts up.

Question: does the lean-from-crankcase-leak theory hold up with these symptoms, or is there something 996-specific I'm missing? Anyone seen the taped oil filler tube produce exactly this "dies with MAF, runs without" behavior? Thank you guys