Okay I have a 3.8 1999 mustang. The problem I am having is all of the sudden my stang is starting to shake really badly and it also does it when it's idling. It really strange because sometime it won't shift until it hits 3grand rpms or a little higher. Also it will just lose power all of the sudden like ill be driving and it won't accelerate foot almost to the floor then bam it goes from 1500 rpms to 3000 rpms and accelerates then back to about 2000 rpms

 

Any codes?

 

sounds like your transmission is failing , or your fuel line is fudged. Tranny places might do a free diagnostics.