Thunderbird idling problem

So I took the T-bird (daily driver) to Autozone to get a new upper plenum gasket cause I was finally gonna get off my butt and put some 24# injectors in the stang I've had laying around for a while. As I put the t-bird in park it starts idling at a little over 2000 rpm's. I turned it off and on one time and it kept doing it. Any idea of what could be wrong? BTW, it's a '93 5.0 about 117K on the clock. Thanks for the help.

Just one more thing to ad. I just drove it and even when I let completely off the gas, it still speeds up slowly. And when I put it in neutral, it goes up to about 2 and a half thousand rpms. It's like I still have my foot on the gas slightly even if I'm not touching it. Does this mean my car just wants to be faster ?

Thanks but I already checked all the stuff like that. I think I might just have to bite the bullet on this one and have someone look at it cause I'm stumped.