Ford Repair: What causes my van to accelerate on its own?, engine computer, ecm

Question
I have an 89 Ford E-150, 8 cyl., automatic with about 173,000 miles on it.  It has started accelerating on it's own even when I take my foot off the gas pedal.  I put it in neutral and it raced for about 20 seconds and then dropped to a normal idle.  I tried tapping the gas pedal but it didn't seem to make a difference.  I drove it this morning again to see if it would do it again.  I drove 3 miles to the end of our road, no problem..turned around and started back and it started accelerating on it's own again..I had to put it in neutral before I could brake and stop.  Otherwise it was like putting your feet on the brake and gas pedal at the same time.  Any ideas?
Thank you for your time and hopefully, your help.
Kerry

Answer
Hello and thanks for the question...I'll try to help.
The last time I saw something like that was in an early Explorer. Needless to say the ECM needed to be replaced. I would have the engine computer system checked for fault codes and go from there.
Erik