that definitely could be, and probably is, causing the issue.
If your throttle position sensor is still there, try reconnecting it and see what happens.
If you're still having problems, pull codes from the computer by running a self-test and write them down:
Checking your Ford Mustang computer codes. You should probably do this anyway regardless if you're still having problems or not. It will tell you if you have other problems.
You'll probably get a code saying something is wrong with the throttle position sensor, regardless if it is bad or not, since it was disconnected for so long. So if you do, I'd reset the computer then take a 2-5 mile drive (with the tps connected if you can) and check the codes again to see if it's still your throttle position sensor.
To reset the codes on the computer, follow the procedures to perform a KOEO (key on engine off) test (in link above), then remove the jumper wire from the self-test connector when the dash starts displaying the codes.
All of this is also described in a 1994 mustang Haynes repair manual which would be a very good thing to purchase.