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DOHC - 2.3L Duratec / Mazda L Engines Discussions and Topics specific to the Duratec 4 cylinder engines

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Old 02-09-2014
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Start up RPM

I just bought a 2009 Ranger with 17825 miles. When I start it cold the RPM goes to about 2500. It gradually drops down but it takes 2-3 minutes. Is this normal for a Ranger 4 cyl.?
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Old 02-10-2014
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It is normal for any fuel injected engine to start up at high RPM.
But 1,500 is more the range.
After a few seconds it should drop to about 1,000 cold, 750 warm.

Fuel injected engines can't use a manual choke plate, no jets to suck gas out of.
So they use an electronic choke run by the computer.

On startup computer opens Idle Air Control(IAC) valve, on upper intake or air cleaner.
The IAC valve is a computer controlled "vacuum leak", it allows extra air to come into the intake past the closed throttle plate.
An idle screw won't work well with fuel injection, because of varying air temp and pressure.

So on startup there is a big "vacuum leak" which raises RPMs.
The computer uses the ECT sensor to get the current engine temperature, this is a simple two wire resistance sensor, so can be tested with OHM meter or Volt meter.
Similar but different ONE wire sender is used for the dash board temp gauge.

If ECT reports cold engine computer closes IAC valve a bit to lower RPMs to 1,000, as ECT heats up computer lowers RPMs accordingly until "normal" RPMs are set, approx. 750.
Your ECT seems to be working since RPMs are dropping with warm up, and the IAC seems to be working because idle IS going down.


In very cold weather RPMs could be higher, but 2,500 seems excessive.

The IAC valve is a mechanical device and can be removed and cleaned, like most sensors and controls(IAC is a control) they rarely fail, but connectors get dirty and so do valves.

Do you get 750-800rpms once engine is warm?
Automatics tend to have higher idle RPMs

You can reboot the computer, this will make it relearn sensor and control parameters that may have changed over the years.
Unhook negative battery terminal for at least 5 minutes, at the next restart computer will reboot and retest all sensors and controls.

Last edited by RonD; 02-10-2014 at 01:26 PM.
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Old 02-10-2014
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The truck is automatic, it the rpms drop to about 900 I'll try rebooting the truck only has 17,000 miles on it. I've had efi trucks before but never a 4 cyl. 16 valve
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Old 02-10-2014
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Yes, saw the miles, less than 5,000 a year, those can be a PITA because of dried out seals and cracked hoses.
They either sat for long periods or were driven short distances so never warmed up enough to get the moisture out of the oil.

4cyl shouldn't matter.

900 is too high for warm idle.
Once warm I would shut off engine, then disconnect IAC valve's connector.
Restart and see what idle is at, if it is still high, 900, then there is either a throttle problem, bad cable or adjustment, or vacuum leak somewhere.
If idle drops to 500-600 then clean IAC valve.
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