A 6.7L Power Stroke that stays parked at 1,100 to 1,200 RPM and will not settle to its normal warm idle around 650 to 750 RPM is either doing something on purpose or reacting to a fault. The trick is telling a commanded high idle from a broken one. Here is how to read a 6.7L that will not idle down, ordered from most to least common.
Why a 6.7L Power Stroke holds a high idle
Most of the time the PCM is raising idle deliberately, and only some of the time is a sensor or control at fault. Common causes:
- Cold engine fast-idle warmup - a normal cold morning bumps idle up until coolant temperature climbs. If it never comes down, suspect a stuck-open thermostat that keeps the engine cold.
- Active DPF regeneration - the truck raises idle during a parked or driving regen to build exhaust heat. Check for the regen or exhaust-filter-cleaning message before chasing a fault.
- Fast-idle / high-idle switch or upfitter control left engaged - PTO, a snowplow control, or an aftermarket fast-idle module can command it.
- Coolant temperature sensor fault - a sensor reading cold makes the PCM hold warmup idle indefinitely.
- Accelerator pedal position sensor or throttle fault - a stuck or miscalibrated pedal signal can raise idle and set codes.
- Brake or clutch switch and safety inputs that the idle strategy uses.
How to diagnose it
- Look at the dash first - a regen or warmup message explains a temporary high idle with no fault.
- Scan for codes and watch coolant temperature live; if it never reaches operating range, the thermostat or coolant sensor is the reason idle stays up.
- Confirm any PTO, fast-idle, or upfitter switch is off and unplug aftermarket idle modules to rule them out.
- Watch accelerator pedal position at rest - it should read zero; a non-zero or jumpy value points at the pedal sensor.
- Check brake-switch and safety inputs in the data stream.
Fixing it
If the engine simply never warms up, a stuck-open thermostat is the usual and inexpensive fix, and it will also improve heat and fuel economy. Replace a faulty coolant temperature sensor that is lying cold. Turn off or repair any PTO or fast-idle control, and remove or correct a misbehaving aftermarket idle module. A faulty accelerator pedal sensor gets replaced and the idle relearned. Do not assume the high idle is broken during a regen - let the cycle finish and confirm it drops afterward. Clear codes after any repair and verify idle returns to spec warm.
Frequently asked questions
Is a high idle on a cold morning normal?
Yes. The 6.7L raises idle to warm up faster and comes down as coolant temperature climbs. If it never drops, look at the thermostat and coolant temperature sensor first.
Does the 6.7L raise idle during a regen?
It does. A parked or driving regeneration bumps idle to build exhaust heat. Check for a regen or filter-cleaning message before treating the high idle as a fault.
Can a bad pedal sensor cause a high idle?
Yes. A stuck or miscalibrated accelerator pedal position sensor can hold idle up and set codes. Confirm pedal position reads zero at rest before replacing other parts.
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