I have Tiagra 9 speed STI shifters on my road bike. The trim feature stopped working on the front derailleur. Pushing the lever after a shift does nothing to further move the FD. Is this a shifter issue or FD issue? Is this something I can fix on my own or do I need to take it to the shop? Thanks.

What you are experiencing is probably a "stretched" cable or a change in setup. I would reset the derailleur using the instructions found at www.parktool.com. They should be performed in sequence leaving nothing out. You can also try hosing out the shifters with WD 40. It is possible that you need new cables and cable housings.

If that doesn't work
I had some older Brifters which also could not do the trim shift after a while and eventually got spotty on the upshift to the larger ring.
Happened to mention problem to a Shimano sales rep at an event.
He said that Brifters do accumulate dirt in the mech. after time and causes spotty shifting... and the lube used in them does get gunky also...

What he claims he didn;t say... : relubing the Brifter can also be a spotty thing - so spray the crap out of the Brifter internals with WD40 - will remove gunked lube and all the accumulated crappage - shifter should work like new...

I did exactly what he claims he didn;t say... Worked like a charm! Brifter was again shifting like new. Have only had to re-apply treatment once in the past 2 seasons, and they still work great.

worth a try - no harm no foul if the brifter is already spotty...