yeah, so i lost my owners manual and was wondering if 89 octane is okay for the ES. my friend said it might leave carbon buildup, but i think he's full of it...

 

Your friend is full of it. Do a search about octane. Moving to a more appropriate forum.

 

Ah hell...this one again. Long and short of the millions of threads containing the word "octane" for dealing with USDM Lancers: 89 is just fine. Yes, it was supposed to rhyme.

 

Your friend is smarter than the average bear. Go dig through the octane posts to read both sides of the story.

On a related note, I think all the forum members posting pics of pitch black spark plugs taken out of their lancers at 10k should tell us what octane gas they run in addition to their city / hwy / track driving mix.