Most likely this problem is your coil. If you are unable to change this yourself, you should take it to a mechanic as soon as you can.
Usually a misfire.
Cylinder #3 misfire
Misfire on Cylinder #7
1-----2-----3 4-----5-----6 -----front-----
On a 2004 Ford Freestar ( 3.9 and 4.2 liter V6 engines ) firewall 1-----2-----3 4-----5-----6 front of vehicle > driver
On a 2004 Ford Freestar , 3.9 ( and 4.2 ) liter V6 engine : firewall 1-----2-----3 4-----5-----6 front of vehicle > driver
Cylinder #2 misfire. see link below
replace the coil bar and you are set
Trouble code P0300 means: Multiple Cylinder Misfire Trouble code P0302 means: Cylinder 2 Misfire Detected Trouble code P0303 means: Cylinder 3 Misfire Detected I would change plugs and wires
This means that your vehicle is missing on cylinder 3. You will need to have your coil changed to fix this problem
Misfire detected in cylinder #7.See related questins for more info.Misfire detected in cylinder #7.See related questins for more info.
Cylinder #1 misfire.