FA20DIT intake valve carbon deposits (direct injection)
Added · Updated
What causes "FA20DIT intake valve carbon deposits (direct injection)" on the Subaru WRX and STI (VA, 2015-2021), and how is it fixed?
A tuning guide says the WRX's direct-injected FA20DIT does not wash fuel over its intake valves, so deposits can build, and calls this a diagnostic lead rather than a defect every engine has. Fix: Diagnose first (misfire data, compression, a look at the valves) before paying for walnut blasting; the guide says fuel additives cannot reach the intake valves on a direct-injection engine.
Symptoms
Varies from car to car; the guide treats deposits as one cause to confirm or rule out, not a predicted failure.
Cause
A tuning guide says the WRX's direct-injected FA20DIT does not wash fuel over its intake valves, so deposits can build, and calls this a diagnostic lead rather than a defect every engine has.
Fix (summary)
Diagnose first (misfire data, compression, a look at the valves) before paying for walnut blasting; the guide says fuel additives cannot reach the intake valves on a direct-injection engine. Single source.
Related build entries
Other VA problems
- Recall 16V-162: turbocharger air intake duct can crack (2015-16 WRX)
- Recall 22V-522: backup light switch can corrode (2015-21 WRX)
- Recall 21V-587: low-pressure fuel pump can fail (2018-19 WRX)
More for this car
- All Subaru WRX and STI (VA, 2015-2021) fitment answers · VA common problems
- Newsletter archive: past issues with every new and corrected entry
Sources
- FA20DIT Common Problems and Reliability: 2015-2021 Subaru WRX — ThinkTuning (tuning guide site, updated August 13, 2026) (editorial; read 2026-10-26; full page read)FA20DIT intake-valve deposits possible; diagnose before walnut blasting; additives do not reach the valves.
Summaries are in our own words. Not repair instructions; consult the factory service manual.
Report a correction — spotted an error or have a better source? Email hello@chassisdex.com.