Went from 93 octane down to 87 yesterday. Retuned it right before I started pumping in the gas with brents 87 tune.

Seemed alright, but started to idle rougly around 500 rpms from then on. Retuned it this morning and bumped the idle and drive rpms up 50 to 900.

Drove fine to school, but started idling at 600ish after a few minutes of driving.

Any tips/help guys? LOL

 

bump. C'mon guys...

 

the octane level shouldnt make it idle rough, it might ping under load if running too low octane. is it missing?

 

I'd reload the tune and, if that doesn't solve it, run the tank down and refill at a different station. Then go from there.Occasionally it takes our PCM's some time to adjust.

There was a recent thread in one of the 2005-2008 forums about a low idle condition after replacing the battery. A sequence of key turns followed by a 10 mile "relearning" ride was provided that resolved the guys low idle condition. Couldn't hurt to find it and give that a try.

Oops... Found it right here in the 4.6L Specific Forum: https://mustangforums.com/m_5038669/tm.htm

 

Itoo recently went from Brent's 93 to the87tune. Idid not experience an ongoing roughness or idling problem though. I have noticed that when changing tunes it does take some time for the engine to re-adjust. I have gone from 93 to stock and back and forth a couple of time and while doing that I didget some rich exhaust, fuel smelland occasional rough idle, but only immediately after the change in tune(s). After a quick drive it always returned to normal operating parameters.

 

That mostly fixed it.

The RPM's used to jump from 400 to 500 while I was coasting and then were 900 while I was standing still. Now it holds steady at ~800 while coasting and ~850 idling at stop lights!