Methods for determining an irregular fuel request (IFR) for vehicle engines coupled to driveshafts via clutched transmissions are provided and include: determining an idle condition of the engine, generating one or more fuel requests during the idle condition, and determining an IFR based on a clutch control parameter and a fuel request generated during the idle condition. The idle condition of the engine is determined based on a vehicle speed and an engine speed if the vehicle speed and engine speed are below respective thresholds. An IFR is determined if a fuel request falls outside a range, and/or if the clutch control parameter is such that the clutch does not substantially impart load to the engine. The idle fuel request range is determined based on a combustion mode of the engine and/or a gear state of the transmission. The method further includes implementing a control action after determining an IFR.