Circuit Description

PCM controls idle speed by adjusting an Idle Air Control (IAC) valve to a calculated RPM based on sensor inputs and actual engine RPM. PCM moves IAC pintle valve in or out to vary amount of air flowing into intake manifold, and thus decrease or increase idle RPM. PCM commands IAC in counts. A higher count allows more air to by-pass throttle plate (higher idle). When PCM detects too low of an idle speed and is unable to adjust idle speed, DTC P0506 will set and MIL will be illuminated on second consecutive trip this is detected.

Conditions required to set DTC are:

• Engine run time is more than 125 seconds.
• No ECT, EGR, IAT, MAP, TP or VSS sensor DTCs set.
• BARO is greater than 72.7 kPa.
• Canister purge duty cycle is greater than zero percent.
• ECT is greater than 122°F (50°C).
• IAT is more than -40° (-40°C).
• MAP is less than 60 kPa.
• Throttle is closed.
• Ignition voltage is 9.5-16 volts.
• Engine speed is 100 RPM less than desired idle.
• Listed conditions are met for greater than 10 seconds.