Stop in for a cup of coffee

zkx14 said

That's how I thought they all worked. Why wouldn't it just be in the computer? If it's already there anyway, what part needs to 'learn' the idle. I don't get it.

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They have a base idle. Iac is a stepper motor. Whilst cranking the ecu looks at throttle position and coolant temp and mass air flow.if voltage drops below the 10 volt threshold the sensors feed the ecu false readings. It wont correct until is has a proper drive cycle.
Which involves a cold start.
Weak battery wont support a good clean drive cycle.