High Air-Fuel Ratio Reading 18-19 - Wideband Gauge Misinterpretation

After an engine replacement, the owner observed air-fuel ratio readings of 18-19 on a wideband gauge and believed the engine was running dangerously lean, despite the car running smoothly with no hesitation or drivability issues.

The owner was misinterpreting the wideband AFR gauge readings. They assumed the ideal 14.7:1 stoichiometric ratio should be displayed at all times, including idle and deceleration. In reality, AFR of 18-19 during coasting and deceleration is completely normal due to fuel cut. The car was running correctly the entire time.

Moderate confidence — Original poster confirmed this resolved the issue