1986 Ranger IAC issue?

[Muzzlebrake]

Hey guys, I have a problem with cold starting my 86 Ranger. It idles high like you would expect but it continues to idle high for at least 5 minutes before settling down to the normal idle speed. Could it be the IAC either sticking or not functioning properly? Any opinions on this? Thanks.

 

[RonD]

No probably not the IAC Valve, if it was sticking it would usually stick more randomly and stay stuck.

IAC Valve is operated by the computer, computer also reads coolant temp from the ECT sensor and RPMs from TFI module.
Computer opens IAC Valve all the way when you turn the key on.
After engine starts, computer starts to close IAC Valve to set RPM based on Coolant temp, the colder the temp the higher the idle RPMs.
As engine/coolant warms up the computer will lower the idle bit by bit.

A sudden drop after 5 minutes could be IAC valve sticking but why would it unstick at almost the same time each time?
IAC Valve is not hard to clean.

More like ECT sensor is jumping from cold to warm
ECT sensor is not expensive, $5-$8, and not hard to change.
ECT SENSOR has TWO wires connected
ECT SENDER just has ONE wire, it is only for the dash board temp gauge

So make sure you get and change the right one.

 

[Muzzlebrake]

No probably not the IAC Valve, if it was sticking it would usually stick more randomly and stay stuck.

IAC Valve is operated by the computer, computer also reads coolant temp from the ECT sensor and RPMs from TFI module.
Computer opens IAC Valve all the way when you turn the key on.
After engine starts, computer starts to close IAC Valve to set RPM based on Coolant temp, the colder the temp the higher the idle RPMs.
As engine/coolant warms up the computer will lower the idle bit by bit.

A sudden drop after 5 minutes could be IAC valve sticking but why would it unstick at almost the same time each time?
IAC Valve is not hard to clean.

More like ECT sensor is jumping from cold to warm
ECT sensor is not expensive, $5-$8, and not hard to change.
ECT SENSOR has TWO wires connected
ECT SENDER just has ONE wire, it is only for the dash board temp gauge

So make sure you get and change the right one.

I never even thought about the ECT! Thanks bud! You're 100% right, the IAC wouldn't unstick at a consistent time interval. I appreciate your response!