I’m asking because i’m chasing a weird idle issue, yet again. All it’s doing is idling really low when it’s cold out, and very high when it’s warmer. I just need to know what the PCM takes into account to determine the idle speed from cold start to when it’s warmed up 100%

How clean is your idle air controller?

I just replaced the motor, and the actual body of the IAC is very clean

Check for vacuum leaks.

A good IAC is not cheap($75 ?), but I would replace it and go from there

Is that the entire assembly, including the valve? Because I got the motor for 30 bucks about.

I'm not sure what you mean that you only replaced the motor. The IAC is one piece. It looks like this:




Make sure the cavity in the throttle body is also clean. If you haven't already done so, clean your TB thoroughly as well.

Thats what I got. I also had cleaned it inside and out, let it sit in a vat of parts cleaner, scrubbed and scrubbed and re-surfaced it all.

I did another smoke test today as well, and it seems that the throttle spring is leaking, as well as something near the IAC. I have plans for a 4.0 TB on my 2.5, so that would hopefully solve that leak. Other than that, I don’t see any other leaks after I re-sealed my intake as well.

This is quoted from the FSM on how idle is determined when it’s in closed loop

When the engine is at operating temperature, this is a Closed Loop mode. At idle speed, the powertrain control module (PCM) receives inputs from:
• Air conditioning select signal (if equipped)
• Air conditioning request signal (if equipped)
• Battery voltage
• Crankshaft position sensor
• Engine coolant temperature sensor
• Intake manifold air temperature sensor
• Manifold absolute pressure (MAP) sensor
• Throttle position sensor (TPS)
• Camshaft position sensor signal (in the distribu- tor)
• Battery voltage
• Park/neutral switch (gear indicator signal—auto. trans. only)
• Oxygen sensor
Based on these inputs, the following occurs:
• Voltage is applied to the fuel injectors with the powertrain control module (PCM). The PCM will then control injection sequence and injector pulse width by turning the ground circuit to each individ- ual injector on and off.
• The PCM monitors the O2S sensor input and ad- justs air-fuel ratio by varying injector pulse width. It also adjusts engine idle speed through the idle air control (IAC) motor.
• The PCM adjusts ignition timing by increasing and decreasing spark advance.
• The PCM operates the A/C compressor clutch through the clutch relay. This happens if A/C has been selected by the vehicle operator and requested by the A/C thermostat.

Check for intake manifold leak at the head. Better yet, just tighten the bolts from the center out in a circular pattern.