Has the PCV been replaced, the pcv diaphragm will split open causing a high-pitched noise at idle. Engine at idle, remove the oil cap or dipstick. If the noise goes away, replace the pcv box or diaphragm.
See fcpeuro and IPD info for pcv repair if the above test is true.
ECM-21CC Long-term fuel trim, idling, bank 1. Upper limit, B5254T7
Diagnostic trouble code (DTC) information ECM-21CC
Condition
The engine control module (ECM) receives information from the heated oxygen sensor (HO2S) about the fuel / air mixture. If the fuel / air mixture deviates from λ=1, the short-term fuel trim will compensate for this by adjusting the injection time so that λ=1 is achieved. When the short-term fuel trim makes an adjustment, the integrator median must be adjusted by the long-term trim. The diagnostic trouble code (DTC) will be stored when the long-term trim must be adjusted almost to maximum in the idle range.
The diagnostic trouble code (DTC) can be diagnosed when idling.
Substitute value
None.
Possible source
Too high ethanol content in fuel.
Air leakage in the intake system
Damaged heated oxygen sensor (HO2S).
Fault symptom
Malfunction indicator lamp (MIL) lit.
ECM-950C Engine control module (ECM), idle speed control. Signal too high, B5254T7
Diagnostic trouble code (DTC) information ECM-950C
Condition
If Engine Control Module (ECM) registers that the actual idle rpm (actual value) is over the limit value for a certain time, the diagnostic trouble code (DTC) is generated.
Substitute value
None.
Possible source
Air leakage in the intake system.
Fault symptom
Malfunction indicator light (MIL), on
High idle speed
Uneven idle
ECM-304C Rear knock sensor (KS). Signal too high, B5254T7
Diagnostic trouble code (DTC) information ECM-304C
Condition
In certain operating conditions the engine control module (ECM) checks the signal from the rear knock sensor (KS). The diagnostic trouble code (DTC) is stored if the signal from the rear knock sensor (KS) is too high in these operating conditions.
The diagnostic trouble code (DTC) can be diagnosed when the engine is running.
Substitute value
Safety retardation of ignition advance
Reduced boost pressure.
Possible source
Short-circuit to ground in the signal cable
Incorrectly installed knock sensor (KS)
Damaged temperature sensor.
Fault symptom
Poor performance.
Volvo Ignition Coil Connector Terminal Pin – Genuine Volvo 978262 | FCP Euro
Genuine, OE, OES, OEM And Aftermarket Online Volvo Car Parts Catalog (ipdusa.com)