Since you have not driven it for a while I would first look at the purge valve to be making the noise, it sits right up next to the firewall in front of the drivers seat. That wouldn't change with engine speed, but would make a clicking sound after vehicle sat for a while.
Lifters are a common fault with the 113 engine, especially after it sat for a long while. When defective, they bleed down and make that sound.
The injectors are fairly easy to check. Just pull off the air cleaner and check them with someone inside revving the engine.
And yes, the 10k mile oil changes are probably the major reason for those lifters going bad. The oil passages in the rocker shafts can get clogged and slow/restrict the flow of oil to the lifters.