*Intermittent electrical problems.
*Intake manifold gasket had to be replaced due to coolant used by manufacturer (common V6 issue from what I hear with this automaker)
*Seat cushioning has completely worn and has no support.
*Forget trying to use A/C while driving!
I shouldn't complain a lot because the car has been somewhat reliable without too many major issues, however, most of its use has been on the highway so the mileage is deceiving.
My wife and I took the payments over from my father-in-law when we got married, so it definitely wasn't my first choice anyway, but now that I am the primary driver of the car due to my commute, I have noticed several issues.
The indicator lights in the dash and LEDs on the radio go on and off whenever they please, and the mechanics thus far have found no lasting solution. At this point it's not worth spending more money trying to figure out.
The intake manifold gasket issue was a major issue for me because it is solely due to the coolant that the maker uses in their V6's. You can't switch to something else, and the mechanic told me the coolant will eat through the replacement gasket within another 50k or so miles. That's just a simple engineering oversight to me, but it costs almost $900 to replace.
If you have the A/C on, you lose virtually all engine power. I have to turn the A/C and the fan off when I am on an entrance ramp just to get up to speed.
Overall, the car feels cheaply made (granted, you get what you pay for), and the fit and finish of the interior leaves a lot to be desired with cheap plastics and rough cloth. The seat cushions are completely shot even though I am very easy-going on my cars and give you no support. You can practically feel the springs right through the upholstery.
In summary, I wish I still had my 1999 Pontiac Grand Prix GTP!!!