Hi I have a 2008 Mitsubishi Lancer 2.0 N/A and I noticed on my scan tool the long term fuel trim is high and stays around +8.6-9.7 during idle but rpm raised to 2500 it drops to +7. The short term rangs -0.6-+5.5. The car runs fine. Should look into this? There is no check engine light or DTCs present. I tried checking for vacuum leaks but none found
Mileage?
In regards to vacuum leaks, there are some SNEAKY locations & very short hoses being part of an assembly so it may be worth going over it again.
160,167 miles
Have you checked/replaced the pcv valve or the power brake booster valve?
Both of those can be a cause too & at that mileage it's likely time.
Update: I checked the pcv valve it’s operating properly and the brake booster valve I tested by taking the hose off and plugging it up. The long term still counties to be +10.9 at idle but now when rpm’s are risen to 2000 it drops to +1.9 the short term is reading closer to 0 now
So the short term is steady around zero & the long term is looking better as well? Sounds like you found your issue.
Replace the hose, booster valve & if there's a "T" that as well, then go from there. Should be directly connected to the manifold but leaks can develop at that fitting over time. It's a good idea to check the overall condition of the booster as well, the can rots if you're up north like me, seals fail, etc without loosing your normal braking ability.
Those little leaks can be annoying so instead of one hose/connection, I replace them all that way I'm done with it for the time being.
Also remember it's a Mitsubishi with 160k, I think it was the lancer evos which were a hit around when yours was made but as a brand they've always had issues.
The chrysler k cars had mitsu engines & that cost em.