About 10 months ago my mom's 09 focus was hunting at idle not much just a 100-200 rpms or so most of the time. There had also been a couple times it had died from it but usually it doesn't behave that bad. No cell no vacuum leaks nothing so I put some liqui moly fuel injector cleaner and it helped almost instantly and the car quit acting up for months. Now it is doing the exact same thing again. I'm assuming it's dirty fuel injectors. Is there any additive that we could try for the long term .