You have something drawing power from the battery some thing left on or something shorting out
i have a 2.0L 2000 jetta and it did the same thing, I had to have the throttle body and 02 sensor replaced.
have the engine timing checked. if the timing is wrong the engine will overheat, are you loosing coolant?is the fan working, is the water pump working?
I had the same problem with my 2000 Bug and it turned out to be battery issue. Because my car has been sitting in the parking lot for the winter battery was so weak that blower didn't work. And as soon as I replaced the battery it was working. That might help.
I would definitely change the gas and probably the oil first. Check for spark and fuel getting to the cylinders.
bad battery. if the lights don't work with the car off after sitting overnight, then the battery is not holding a charge and it's time to replace it.
Is the battery/alt warning light on? if they didn't disconnect the battery while the starter was being replaced and they accidently shorted the battery cable out it could have damaged the regulator of the alternator some of the Delphi regulators are very sensitive to that, but if it tested normal at the parts place, does it run down while driving or while sitting?
Something is on, as in headlights or ignition, or the battery has a dead cell. If the battery is over 2 years old it is more than likely the battery itself that is the problem. Disconnect the battery positive cable and fully charge the battery. Let it sit overnight and if it goes dead, replace the battery. If not, find out what is running it down.
If you know it is the battery then try using a charger to charge the battery, make sure that you clean the battery connection terminals. If the battery will not take a charge from a charger then replace it, if a battery gets too dead it can't be revived. Also, have your alternator checked before driving if you didn't cause the problem with sitting or leaving the lights on etc.
Yes you sure can. It is a myth that sitting a battery on concrete will drain the battery. It will not drain it at all.
Purchase a trickle charger and keep it connected to the battery.
Yes. It is a myth that a battery will run down sitting on concrete.
To find the battery you will have to take off the left rear tire. If you removed the panel, the battery will be sitting right there