Reluctant Start -- Would Appreciate Your Expertise on Audi, Seat, Skoda and Volkswagen Tuning Support Forum.

Hi All,
This newbie needs your help, please, with a much-loved but recently balky '98 Passat 1.8T AEB 82k miles (stock, never chipped, sorry so boring). This car will NOT start when either (i) the engine is fully warmed up or (ii) the ambient temp is quite cold (sub-20F). When either of these conditions exist, no amount of cranking will produce even a hint of firing, let alone a start.
The warm non-start problem is a few months old. Once at operating temp (dashboard gauge shows steady 190F), the car will not re-start until it sits for 10-15 minutes (and then it typically fires right up). The coolant temp and manifold temp sensors were replaced, and the air filter checked/cleaned/replaced, with no improvement. I considered bad fuel, but the problem has persisted through several new tankfulls of name-brand premium. Ideas not yet explored are the MAF sensor and the fuel pump.
The cold non-start problem is new, courtesy of recent cold weather. On two occasions when temps dropped to 10F, the car -- which in 12 years has never failed to start instantly during Chicago winters -- would not catch. Both times, I cranked it 15 min until battery death followed by another 15 min with jumps, taking timeouts only to show the starter mercy. Nothing. Success came only when (i) ambient temps went up to 25+F and (ii) I cranked 15+ seconds with the throttle continuously floored (something I tried in desparation since normally I leave the throttle alone when starting a FI engine). When it did start, it was ragged -- first one or two cylinders, then the rest -- but afterwards it ran and drove just fine. On both occasions, after much cranking but before it caught, I got an engine error code P0302 (cyl 2 misfire) which I attributed to fouling ... but what do I know? Once it was running, the error terminated/reset after several normal operating cycles.
A few more factoids: The car continues (even after the above cold non-starts) to get good mileage, 25+mph in town with smart driving. There might be a bit of hesitation on acceleration (apart from turbo lag), but at 3000+ rpm the engine pulls great. There never has been the slightest hint of stalling or power loss once running. One unusual thing is that the car sat for three years (2002-2005) with only occasional use (1-2 times per month); during that time, STABIL fuel stabilizer was used at the high end of (but within) the recommended dosage.
So, any ideas? There's a lot of brainpower and experience here, so I've got my hopes up.
Thanks!