Why this comes first: your ECU's stock ROM is the only perfect record of how your specific car left the factory. Flash tunes over it without a backup and you're depending on strangers' files to ever return to stock. Read it, verify it, archive it in three places. Then tune.
Step 1 — Conditions: battery healthy or on a maintainer, key ON engine OFF, all accessories off (headlights, HVAC blower, seat heaters). Reading is gentler than writing, but clean stable voltage is the habit to build now.
Step 2 — In ECUFlash, choose the read function and select the correct memory model for your car when prompted. ECUFlash generally auto-detects EJ-era ECUs correctly; if it asks, your car's generation and market determine the choice — the ECUFlash documentation lists them, and forums have confirmed configs for every common model.
Step 3 — Start the read and then do not touch anything: no key movement, no door slams, no laptop sleep. Disable Windows sleep and screen-off timers before you start. A read takes several minutes with a progress bar; interruption during a READ is recoverable, but treat it like a write for practice.
Step 4 — When it completes, ECUFlash holds the ROM in memory. Save it immediately with a name you'll understand in five years: something like stock-2004-STI-CALID-A4TC400G-2026-07-19.bin — car, CAL ID, and date.
Step 5 — Verify the file. Open the saved ROM back up in ECUFlash and confirm it loads with the correct CAL ID and that RomRaider (next guide) recognizes it with definitions. A backup you never verified is a hope, not a backup.
Step 6 — Archive in three places: the laptop, a USB drive that lives in the toolbox, and cloud storage. Email it to yourself if nothing else. This file is small and irreplaceable.
Step 7 — Read it a second time and compare file sizes as a sanity check that your setup reads consistently. Now — and only now — you're ready to think about modified ROMs.
Tuning changes engine behavior. Numbers here are typical, not guaranteed — your fuel, climate, and hardware matter, and a professional calibration for your specific car always beats a generic map.