Code PO422 rough idle, stalling

2002 FORD RANGER
281,000 MILES • 4.0L • 6 CYL • 4WD • AUTOMATIC
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ROBERT WHATLEY
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Truck starts and runs at 1100 rpm's but after it warms up the rpm's drop to around 500 and then the engine stalls. Replaced plug and wires, fuel filter, no change. Checked for vacuum leaks using carburetor cleaner, no change in idle or rpm's. At a loss. This is my work truck. Need help.
Nov 28, 2017 at 5:15 AM
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MHPAUTOS
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The most common cause for the P0422 trouble code is a malfunctioning catalytic converter. However, there are a many other issues that can result in the code (or that may cause the catalytic converter to malfunction), including the following:

Faulty oxygen sensor.
Malfunctioning coolant temperature sensor.
Faulty fuel pressure regulator.
Faulty manifold air pressure sensor.
Malfunctioning mass air flow sensor.
Contaminated engine oil.
Engine leaks upstream from the catalytic converter.
Engine is misfiring.
Loose or damaged wires and connectors.

I would suggest that you start checking all in the list above and re post for further assistance if required.
Nov 28, 2017 at 6:24 AM
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ROBERT WHATLEY
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Replaced MAF sensor. No change. Scratch that one off the list.
Nov 28, 2017 at 8:28 AM
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MHPAUTOS
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Unfortunately i cannot give you a suggested line off attack, probably do the least expensive checks first, start small and work up.
Nov 28, 2017 at 10:35 AM
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HARRY P
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At that many miles, I would start with checking the catalytic converter. If it is not welded on (ie it can just be unbolted) I would drop it, take it for a ride, and see if it is better. If it is welded, then I would pull the O2 sensors and again take it for a ride. Yes, it will be noisy. But it is an easy way to check catalytic converter's performance.
Nov 28, 2017 at 10:36 AM
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ROBERT WHATLEY
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Replaced the IAC and that solved the stalling issue. Now I am getting a PO174 and PO300 code. Any thoughts?
Nov 29, 2017 at 8:12 PM
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MHPAUTOS
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P0174 is a code for a Mass air flow sensor and the P0300 is a random engine misfire, this may be triggered by the MAF code so look here first.
Dec 1, 2017 at 12:24 PM
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ROBERT WHATLEY
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Just replaced the MAF before 174 came across. Could it have been a bad one. Got it from AutoZone
Dec 1, 2017 at 5:44 PM
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MHPAUTOS
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not unknown to have a bad new item, just check that the electrical connection is sound and tight and there is no corrosion on the terminal pins.
Dec 1, 2017 at 6:02 PM
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HARRY P
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Yeah it definitely wouldn't be the first time that a sensor from AutoZone was faulty. I'd probably probe the connector though to make sure that it was receiving power and jiggle it around to make sure that the connection wasn't weak. If the connection is ok, then return the sensor and get a new one. Good luck and keep us posted.
Dec 1, 2017 at 6:53 PM
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