First thing I would check is the battery terminals and the small red wire that connects to the positive battery terminal. Since the car has been worked on, I expect that maybe a battery connection may not be tight?
Also get a Voltmeter and/or go to the local auto parts store and have them check the alternator and battery. Usually they do this for free.
How old is the battery? If over 4 years old, just replace it.
Sounds like the car is going into limp mode? Any other lights on the dash? Trouble codes?
Doubt the problem was the throttle body? Be careful where you get the work done, I would back off for a moment on allowing shops to toss parts at the car. I have not heard many 1.8t throttle body problems.
A few more issues.
If you plan on keeping this car, you NEED to do a few things.
1. Purchase an OBDII scan tool, even if you do not know anything about cars, you NEED one of these tools. Less than $50 and it will pay for itself the first time you use it. See first link below in my signature. Ask before you buy, ask if you have questions.
2. Engine temperature, if the engine has a soft thermostat, you are on BORROWED time. The oil pick up WILL get restricted and the oil light WILL start coming on. The thermostat is a $12 part, proper engine temp in these/any cars/car is IMPORTANT. Do not ignore this. See 2nd link below in my signature.
3. With the age and mileage on this car, you NEED to figure out if the timing belt and water pump were ever changed. I doubt it. It is about a $500-$600 job if you shop it. If the timing belt breaks, well, $3500 and a few weeks, you decide.
4. Transmission, well I hate to tell you, the automatic transmission valve body in this car is likely on its last legs. VW extended the warranty on these due to all the problems, but you are beyond even the extended warranty. Problems start as early as 70k miles, and can show up as late as 100k miles. Late/harsh upshifts, harsh/no downshifts. Worse when trans fluid gets warm. The good news is usually the trans are in pretty good shape and a reworked valve body will resolve the problem. Expect to pay between $700-$1100 if you can shop it and/or do the work yourself.
Where are you physically located?
Hate to say it, but as nice as a car that you may have, it is in the high maintenance window and will cost you.
I have a 2003 convertible, bought it new for my wife as a daily driver. At 70k, it was used up. Oil pick up restricted, trans valve body shot, all sorts of window and door latch problems. Everything that could have gone wrong with this car, it happened. Was only offered $5k for the car @ 7 years old. This was a GLX, $28k car.
Decided I was not going to have a car cost me $3200 per year! Hell, could have leased for about this much and walked away after 3 years with few headaches.
So I decided to commit to it and try and get my money out of the car. Have spent money on it, but ALL labor is mine. Have put over 14k trouble free miles on it over the past year. My 17 year old has been driving it and love the car. It is a nice car when working correctly.
Hope for her to get another 4-5 years out of the car. She did hit a BAD pothole and take out the tire, wheel, axle, control arm, but overall the car was not damaged, all parts bolt on replacement and best of all she was not hurt.
These cars can take a beating, but they are also temperamental and need to be maintained.
Hope this info helps?