I have a 95 grandam with issues.  About a year ago, I had a tune up as
my car was running rough.  When I got my car out, it was better for
about a day.  Then it seemed to be worse.
I took it back and they told me it was an unrelated problem, and it was
either the oxegen sensor or the entire computer system.

I thought they were a bunch of goofs, so I took it elsewhere.  I was
told that the sparkplug wires that were put in were faulty so they were
changed.  This really did not help and it was running rough.  The back
end of the car gets black sut all over it from the exhaust.  I was then
told to get the cadillac coverted replaced which cost a fortune.

It never really fixed the problem but it ran smooth.  Very poor on gas
and the black sut still appeared.

Now it has been about a year and the car is running really rough again.
I took it in again and was told that I needed an ERG valve and the
cadillac converter was plugged.  I explained that this was new.  Where
we live, this is not needed so they just by passed it with a pipe.  The
car ran fine, but was very noisy and still a small amount of black sut.
It has been a few weeks and now the car is running really rough again
and the heavy black sut is back.

Can anyone advice me on what to do or what the problem could be.  I
feel like this vehicle is a money pit, but if it is working should
still be worth some money, not working it is not worth anything.

Thanks in advance
Just me