98 Ford Taurus SE Accelerates by itself, what's wrong?

I have a 98 Ford Taurus SE with 20,000 miles on it. I've only put 9,000 miles on it, but the entire time I've owned it it has had an acceleration issue.
Pretty much the car will crawl up to 40mph flat land without pushing on the gas. The car does not idle high or low. It seems to be in perfect mechanical condition, and should be due to low mileage. Before I purchased the car was stored for years very well, all fluids removed and set on jacks stands heated indoor storage.
when I'm driving 60 on the freeway, the car can keep a constant speed. I have driven 10 miles on the freeway without touching the gas pedal. The gas petal feels fine, no issues from what I can tell. The cruise control works fine, and I'm certain it has nothing to do with the issue.
Any ideas? I haven't done anything other than a full tuneup.

First of all, STOP DRIVING it. If you have throttle issues, they can get worse and you can get yourself killed. Go to a ford mechanic and explain the specific problem.

When at Idle the IAC (Idle Air Controller) sets the speed. When you step on the gas it is bypassed. What can affect the IAC is a Vacuum Leak. Check all your rubber and plastic vacuum lines and fittings. Or let a mechanic look at it and/or put a vacuum gage on it.

Replace the idle air control valve, they had a lot of problems.