Ford Repair: 2000 Ford Mustang, mass air flow sensor, mass air flow

Question
6 cylinder 2000 Ford Mustang (3.8 liter) 126,000 miles
My engine is shaking violently! I have changed the spark plugs/wires, fuel filter, changed the transmission bracket (broken), checked the engine mounts (good), changed the mass air flow sensor and although I have to admit it does run a little better but still shakes pretty bad.  I was told to do two other things, put STP (or equal) in fuel tank and also disconnect the battery terminals for ten seconds (due to changing the mass air flow sensor).  Do you have any other ideas what else to check??  Please respond quickly before I sell it and get a Chevy!!!  
Thanxxx!!  

Answer
Larry,

Sell it and buy a Toyota!!!  LOL. It sounds like you may have an internal engine problem such as a burnt valve. This causes the cylinder to not build compression and thus will not do any work throwing the engine out of balance.  

Try this trick. Cut six small vacuum lines about an inch long. Now, place each vacuum line between the spark plug wire and the coil pack. Grab your test light. Start the engine and hook your test light to ground. Now touch each vacuum line/plug wire at time. You should notice an RPM drop on each cylinder. If you have no RPM drop then that cylinder is not working.

Do a compression test on the dead cylinder to verify any problems.

Good Luck!!!