I do use 85, but always used it in my 2018 with the 3.5, so I never thought of that as an issue.

I will try on my next one just to eliminate it as a possibility.

Thanks!

 

High compression motors definitely do not like low octane. Try running 91 and see if it smooths out. Hunting idle can also be due to poor engine/bay grounds. We used to put grounding kits on hondas and the idle would smooth right out.

 

Happened to mine once. It was during an extended idle ( setting up the Sync, etc ) I blipped the throttle and it stopped.

 

Just got my truck about two weeks ago and have put 1k miles on it. I traded in my 2019 3.5L ecoboost and decided to go with the 2.7L ecoboost on the 2021. I have noticed a rough idle about 80% of the time when stopped whether the engine is warm or cold. I never felt any type of shake or rough idle whatsoever from my 2019 which was really smooth I could barely tell it was on. Motor mounts? Maybe another issue. Anyone had this diagnosed at the dealer so I can go to them with some ideas and I don’t get turned away. Thanks.

 

I got a brand new XLT 3.5.

I also notice a little vibration I feel on the brake peddle with stopped while it’s running like a parking lot or drive thru.

don’t really feel it in the wheel and can’t see much rpm bouncing.

just feel it in the peddle more than I’m used to with my last truck a Titan v8.


I figure it’s because I’m running 87.

You know something I bet no one has done a test on yet. Every generation Ford keeps increasing the horsepower and torque of the eco-boost. It’s not magic what they’re doing, they’re basically just tuning it the same way aftermarket tuners can add more power and horsepower.

Long story short, every time you run a tune on a vehicle you usually increase the octane rating.

This is just a guess at this point with no data, it’s a test, I wonder if the new F150’s would prefer to run on high-octane gas even more than the older generation ecoboost. I know a lot of people said it didn’t matter as much with the older generation but maybe this one does matter.


As a matter of fact for me personally, I only noticed this after I filled the truck up for the first time. I really wonder if the dealership put high-octane gas in it when they gave it to me. Because I did not notice it for my first tank. I will probably try some high-octane gas at some point and see.

 

I just filled up last night with 93, I will report back.

 

awesome really interested to hear your findings

 

initial results are good. First cold start this morning ran perfectly smooth. Drove for a bit, seemed more peppy, and smooth somehow even when driving.

Came in the driveway, into park..totally smooth.

I'll report back after driving for a bit, but it looks like my gas cost is going up from now on!!!

 

My opinion is the idle rpms are set at 500. I never saw my 2017 idle this low. I don't personally believe it is octane related. I definitely feel the same vibration.

 

If it is just a SHAKE your good, but if you also get a RATTLE and ROLL you need to get it to the dealer...