Guide step
Visual inspection first
Check intake boots, PCV hoses, brake booster line, and manifold gasket areas.
Guide page
Vacuum Leak Checklist for Lean Codes and Rough Idle
Use this vacuum leak checklist to spot lean-code, rough-idle, PCV, booster, and intake-leak clues in the right order.
Guide step
Use trim behavior as a clue
If lean trim improves off idle, intake leaks become more likely.
Guide step
Smoke if needed
Smoke testing saves time when no obvious split hose is visible.