1999 legacy outback wagon is running bad but when I get the codes read, nothing ever comes up?

Sometimes it runs so bad, the rpms will go up , then
they'll go up and down, the car stutters and hesates
when accelerating.  It stalls and dies, it will always
starts again! The funny thing is , it never shows any
computer codes!   And it doesn't do it all the time!  If I
open the hood and fiddle around, push and wiggle
with stuff ( really )  it runs great after but sooner or
later it starts the same stuff!  I have had it to the
twice, to different shops, one was a Subaru
dealership, he couldn't find anything, no codes but
after he checked out the engine ( moving things
around ) it ran fine for him.  The other place couldn't
tell me what was wrong with it.   I am lost here,  yes I
am a women with not much knowledge about cars
and engines.   Could the computer that gives the
codes be damaged?   Oh and when it going to run
bad, it will start to shift really hard into gears.  It is a
automatic!  Any help or information would be greatly
appreciate!  Thank you.