P1087

P1087 is the mirror of P1086 on Subaru AVCS bank 1 — actual cam advance is LOWER than commanded, meaning the intake cam isn't advancing enough when the ECU asks it to. Same hydraulic system, opposite failure mode. Cheapest-first ladder: (1) Oil first, always. Low oil level, wrong viscosity, or sludged oil are the #1 cause of under-advance because AVCS needs adequate oil pressure (typically 25-45 psi at the OCV feed at warm idle on an EJ25) to swing the cam phaser. Check the dipstick before plugging in a scan tool. (2) Live-data scan: commanded vs. actual advance. On a healthy AVCS engine the actual should reach commanded within 200-400 ms; if actual sits 5-15 degrees below commanded and crawls toward it slowly, the system is oil-pressure or solenoid-starved. (3) Pull the OCV and inspect the screen — same screen-clog pattern as P1086 but presenting as under-advance instead of over-advance because the solenoid is stuck in the retard (rest) position rather than stuck advanced. (4) Test OCV duty cycle response with the scan tool: bi-directional control should sweep the solenoid from 0% to 100% duty and you should see actual cam advance follow within 1-2 seconds; a stuck OCV won't move regardless of commanded duty. (5) Resistance-check the OCV: 6.9-7.5 ohms cold on EJ-series; out-of-spec means replace. (6) Final and most expensive: AVCS cam sprocket assembly internal wear — the lock pin and vane seals inside the phaser degrade and let oil bypass without rotating the cam. Don't condemn the cam phaser hub before verifying oil pressure at the OCV feed port — a worn oil pump on a high-mileage EJ25 starves AVCS at idle and creates a P1087 that looks identical to a bad phaser.

Vehicle-specific patterns: 2003-2012 Subaru Forester/Outback/Legacy/Impreza EJ25 SOHC is the volume P1087 platform — same oil-screen clog story as P1086 but stuck in the retarded position; clean the screen, change the oil, reset, and most clear. 2008-2014 Forester XT and 2008+ WRX/STI with EJ255/EJ257 turbo dual-AVCS see P1087 most often after a botched timing belt service where the AVCS hub was installed without proper alignment to the cam pin — the cam reads physically retarded relative to where the ECU thinks it should be. 2013+ FA20 (BRZ/WRX) is less common but when P1087 hits, it's usually paired with a low oil pressure complaint and points at the oil pump or pickup screen rather than the AVCS itself. 2011-2018 FB25 (Forester, Outback, Crosstrek 2.5) sees P1087 from timing chain stretch retarding the entire intake cam baseline, especially on 110,000+ mile engines run on long oil-change intervals; borescope the guides before throwing parts at the OCV. Estimated repair: $80 (DIY oil + screen clean) to $1,800 (timing chain + guides + tensioner on FB25).