If you put the car in park rev the engine to 3,000 or so ( not much higher ) . Let off the gas and you hear a knock as the engine returns to an idle, you have a bad rod bearing. If it knocks only on a cold start, you could have a collapsed piston (skirt).
With the engine off pull your intake elbow off the throttle body and have someone else push the gas pedal to the floor. Check to see if the throttle body is opening all the way. I've seen two aod's mustangs that weren't fully open.
You don't need a code scanner to read any hard or soft codes on your car. If you look in the driver's side of the engine compartment by the firewall. You should see a plug ( the self test output, it should have a cap over it ) that has 2 connections (top ) and four connections (bottom).
It looks like this :
` _ _*
_ _* _ _
All you need to do is put a paper clip, wire or needle nose pliers in the top right and bottom second from left spots. Then turn the ignition to the on position. The eec will run a self test and the MIL light ( Malfunction Indicator Light - check engine ) will flash any stored codes. There will be a two second pause between digits and a four second pause between codes. You may have to do this more than once and you should have the engine up to running temperature before you stat the self test.
The are running tests you can perform as well.