Engine stumbles/firing problem?

More problems with wifey's car... but what's new? And why do we always have problems on trips?

01 Jetta TDI, for reference.

About two hours from home, I notice that the engine is suddenly starting to limp. I driving about 70, and power just drops. Won't accelerate no matter where the pedal is. So, I start to pull over, and the power catches and the car shoots off like a rocket. Same thing happens for a mile or so before I can pull over. When I finally do, it dies before we can stop. Won't restart; just cranks. Pedal on the floor finally starts it and barrels unburned fuel out of the exhaust in a cloud of smoke. We slowly limp home to swap cars. I can't believe we made it home.

Cliff's Notes:

Sudden periodic power loss during that begins (usually) during decelerations.
Periodic shuddering at very low speeds/stop.
Unburned fuel is exhaust.

Feels like it's not firing on all cylinders when it does it at low speeds. Then, it starts firing and burns away all of the excess fuel. It's just on and off, and it's driving me insane.

After all the recent trouble I've had, I'm starting to hate this car. Aircooled FTW

Couple things. You need to get the car to a guru, a good one. Where are you? How many miles on the car? Has the intake been cleaned? Recent timing belt? If so who did it? You could have dropped or are dropping carbon in to one of the valves and holding it open. No compression, lots's of unburnt fuel violent rocking of the motor until it breaks it or burns it off. Or, worse case, the injectors were so dirty it was a bad spray patteren and it melted a piston and you have no compression.

But, it could be a simple thing, but it does not sound like it.

Good luck.....

I'm in Oklahoma, so I'll be taking it to Dallas. Car has 135k on it, and 60k on the engine (broken timing belt=bent valves=new(ish) engine). Timing belt was recently done, and I've already contacted the shop where it was done. Labor is under warranty, and the engine is still under warranty from the swap.

I don't have a valve stuck open or a melted piston since the car runs smoothly about 65% of the time. It's the rest of the time that I start having problems and the car isn't hitting on every cylinder. Like I said, it's intermittent.

Fuel filter? Injection/dictributer pump? Something electrical? I'll trailer it to a shop this weekend on next week. I'd just love to have some insight before I get there.