2018 Ford Edge 3.5L - idle is not so smooth

[bhamraS97]

Hi All,

I have been noticing that from last 4 fills I have been using 91 octane but with 91 octane I find that the idle is not so smooth and there is shutter from 1-2 gear more on low speed specially when accelerating on 2nd gear.

I thought it might transmission, I re-did the fluid change before 20K kms, the fluid that came out still clean. But even after oil change I felt the shudder.

 

So I went back to using 87 octane, and from last 2 fills, the engine idle again smooth and rarely shutter occur depending on throttle input.

I know that 3.5L is a low compression engine but I felt 91 more responsive (probably placebo)

 

Any idea why would that be or anyone experienced shudder?

[MLTEdge]

While I have the newer v6, a lot of people here say burn only 91octane. I use 87 and it runs perfect. I towed once or twice and did use 91 for that, but otherwise the car runs perfect on 87. My manual says designed to burn 87 octane, no lower, but "recommended" is 91. I understand 91 better under harsh conditions, but otherwise it seems not needed. Conspiracy people will tell you the oil companies get them to raise the recommended octane, others just because it may ignite more controllably, but fact is manual says engine designed to burn 87 octane. That may be why it runs better 

[enigma-2]

Engine needs a slight amount of knock to determine where the rich/lean setting is. Without knock, ecm defaults to a rich setting to protect the engine. MPG falls as well. 91 octane blocks knock and knock sensors can't send signal.