Detection Condition

WARNING: This page is about a different car, the 2002 Mazda B4000, 2002 Mazda B3000, and 2002 Mazda B2300. However, it is still accessible from the selected car via links, so may be relevant.

DTC P1518 indicates intake manifold swirl control is stuck open when signal on the monitor pin is less than an expected calibrated range at closed throttle.
DTC P1519 indicates intake manifold swirl control is stuck closed when the signal on the monitor pin is more than an expected calibrated range with IMSC activated.
DTC P1520 indicates swirl control output circuit malfunction.

Intake Manifold Swirl Control (IMSC) consists of a manifold mounted vacuum actuator and PCM controlled electric solenoid (swirl control solenoid valve) with linkage from the actuator attaching to manifold butterfly plate lever. Each engine cylinder has a single air passage with a butterfly plate that blocks 60 percent of the opening when actuated (less than 3000 RPM), leaving the top of passage open to generate turbulence. The housing uses a return spring to hold the butterfly plates open (when not actuated). The vacuum actuator houses an internal monitor circuit (swirl control motor) to provide feedback to PCM indicating butterfly plate position. When engine speed is less than 3000 RPM, the vacuum solenoid will be energized. This allows manifold vacuum to be applied and the butterfly plates to remain closed. When engine speed is more than 3000 RPM, the vacuum solenoid will be de-energized. This allows vacuum to vent from the actuator and the butterfly plates to open.