Car trouble- PLEASE help...

To start with, it's freezing outside. I don't know if that could be a factor, but I'm praying that's all it is. Anyway, I have. 1999 v6 cougar and am having some serious problems.
Over the past few days, I've noticed that when I am sitting with my foot on the break, at a red light for example, the car rocks back and forth like crazy. The first time it happened, I turned the car off and back on and it quit. The second time it seemed to weaken and eventually stop just as I drove it. Then today I tried to drive it and it all just went to pot. I noticed that when I would press the gas pedal it wouldn't move at all for a couple seconds, then would shoot forward and still felt like something was holding it back if I push the pedal when moving. Then when I hit the brakes, it would barely stop, and still move forward with the pedal all the way down for a couple seconds. Then it would do the rocking back and forth thing. I don't have a clue... It sounds like a brake issue to me minus the red light bit. My friend who knows quite a bit more about cars than me says it sounds electrical. I don't know what to do...

Back to the basics. When was the last time the vehicle had a tune up, including fuel and air filters? It could be that simple.

Honestly, I don't know. I just got it a couple of months ago and I haven't done anything to it, really. Had trouble with a fuse messing with locks and the brakes when I first got it, but that's about it, and that was fixed. The guy I got it from claimed it had been recently tuned up, but you know how that can go.

It could be something to do with a vacuum leak. The brake issue is similar to the brake booster losing vacuum. I would still look into the tune up. maybe remove a plug to see what it looks like.