[s-cars] List advice needed

[Realcoast at aol.com]

93 S4
Problem :
Studdering type miss, when cold or warm
up to usually 3000 + rpm but not always goes away.
The symptom can disappear entirely for 30 + km at any time.
Began immediately after changing fuel pump and filling tank to check the  
seal.
I have run water remover thru and changed filter and plugs to no  avail.
Best guess- electrical ?
Any input much appreciated.
Dave H.