94 thunderbird code 1505

Diagnostic Trouble Code (DTC) P1505 indicates the IAC system has reached the adaptive clip.
Possible causes:

• Air leaks.
• Plugged air filter element.
• Throttle body/linkage binding.
• Contaminated or damaged IAC valve assembly.
• Damaged throttle body

The Adaptive Idle Air Control (IAC) strategy is designed to adjust the IAC calibration to correct for wear and aging of components. When engine conditions meet the adaptive strategy learning requirement, the strategy monitors the engine and determines the values required for ideal idle calibration. The adaptive strategy stores these values in a table for reference. This table is used by the PCM as a correction factor when controlling idle speed. The adaptive idle table is stored in Keep Alive Memory (KAM) and retains the learned values even after the engine is shut off. A Diagnostic Trouble Code (DTC) is output to indicate that the adaptive IAC strategy has reached its learning limits.
Whenever an IAC component is replaced or cleaned or a service affecting idle is performed, it is recommended that KAM be cleared. This is necessary so the idle strategy does not use the previously learned adaptive values.
To clear KAM, refer to PCM Reset in Section 2. It is important to note that erasing DTCs with a scan tool does not reset the adaptive idle table.
Once KAM has been reset, the engine must idle for fifteen minutes (actual time varies between strategies) to learn new adaptive values. Idle quality will improve as the strategy adapts. Adaptation occurs in four separate modes. The modes are transmission select in neutral with air conditioning on; transmission select in neutral with air conditioning off; transmission select in drive with air conditioning on; and transmission select in drive with air conditioning off.