I have the same problem with Tiagra STI shifter and FD. The inline barrel adjuster does not have any effect on the cable. I'm going to try to reconnect it to the shifter holding the housing. Original OP you don't mention if that solved your problem.
Originally Posted by
tass1
Update. The barrel adjuster was slipping as AEO mentioned. Held on to the housing on one side and gave it a quarter turn. Rode 50 miles on saturday and it didn't happen once. Made a point to shift harder as Al mentioned, also. And I've walked the entire cable and that is the only adjuster for the front derailleur.
Thanks again.