Engine High idle for 5 min every start

[BurnsTremor81]

My dads 3.5 has been hanging a high idle for extended times. Over 1000 rpm, its actually trying to push through the brakes at stop lights. This is not the normal warm up high idle, it seems to be much longer.

Anybody else ever had this? Truck runs fine otherwise and will eventually idle down. Until the next restart. He is claiming that it does it ever restart regardless if the engine is warm.

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[Borchelt]

Does your Dad drive a PowerBoost? The only time I see a high idle is when the system needs to charge the battery pack for the inverter.

 

[BurnsTremor81]

nope just a standard truck. i think it has the 400w inverter outlet in the bed.

 

[rpold150]

You're in a lot colder weather than I am, so that could have something to do with it. But 5 minutes seems very long. My high idle is only for about 20 seconds, and then goes down to something like 800.

 

[BurnsTremor81]

yea thats what im saying. My tremor is less than 30 seconds id say. And it hasnt been that cold out yet.

 

[NiftyF150]

I had my truck sitting outside in very cold weather here in Minnesota about a week ago and it also had a high idle for almost 5 minutes before it finally dropped down. It's pretty noticeable on my truck with the resonator delete. It's louder on a cold start at idle than it is when it's up to temp and driving.

I'm guessing it has to do with emissions. The high idle is to warm up the cats for them to function properly as far as I know. Perhaps the warm up cycle for the cats continues until the rear o2 sensor determines that they are at operating temp and meeting emissions?

Hopefully someone with more knowledge than me can chime in here.

 

[reybeast]

I have a 2024 F150 3.5 eco, it idles at 1400 rpm on cold start. It seems it stays that way until coolant temp is ~145 degrees. They loaned me a 2025 Explorer with a 2.x liter eco, and it also idles at 1400 cold.

 

[timnohio]

My dads 3.5 has been hanging a high idle for extended times. Over 1000 rpm, its actually trying to push through the brakes at stop lights. This is not the normal warm up high idle, it seems to be much longer.

Anybody else ever had this? Truck runs fine otherwise and will eventually idle down. Until the next restart. He is claiming that it does it ever restart regardless if the engine is warm.

Did you ever find out if there was an issue?
90 degree day today in Ohio. Cold start rpm is around 1200. We have a slight decline in our driveway to the road. I idle down the driveway to the road and it revs up while I'm pushing the brakes. So much that I out it in neutral today. Today was worse because it is now tuned and it was revving up a ridiculous amount.
I get out on the road where it's flat and it feels like the cruise control is on. I let off the gas pedal and it just keeps that speed by itself with the cruise control off for a good 5-10 seconds.

Anyone know what this could be?

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