Engine idle won't come down

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Sep 15, 2018 | 10:48 AM

Flynman

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Joined: Apr 2018

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Engine idle won't come down

2018 Lariat F350 Super-duty 6.7 4000 miles..Parked the truck last night and everything was fine. Started up this morning and I noticed idle seemed a little higher around 1300 RPM's (outside temp 80 Deg.) Then after driving it for a few minutes I noticed that Truck was going 50 mph without stepping on the gas. When I pressed the Brake a message came up saying " brake Applied Power Reduced" I put the Truck in Neutral and it was idling at 2200 RPM and then when I stepped on the brake it went down to 600 RPM. When at a light with my foot on the brake it idles normal but once I start rolling idle goes up and truck will do 50mph by itself?? I don't have any high idle mods or anything like that.

Thanks,
Keith R

Sep 15, 2018 | 11:03 AM

C12H24

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I'd first check for some obstruction with the throttle pedal...like a floor mat or something stuck in the throttle return. You should have an error code show up and the truck go into a limp mode when there is a disagreement between the throttle pedal and the injector pump commanded flow (or throttle position sensor for gassers). Without that code and limiting behavior, I'd look for that obstruction. There is also a safety step involved in this and it is referred to as "brake over throttle." What this means is if you are pressing on the throttle and step on the brake at the same time, the system will null the commanded throttle position and idle the engine.

It should go without saying that you shouldn't be driving the truck under these conditions. It is a dangerous situation.