I've been running 93 octane for awhile now, but since I was kind of low on cash at the moment, I filled her up with 89 octane. As I pulled up to my house and put it in park, my engine's idle was not the usual smooth idle i'm used to hearing. it's something like

" *smooth idle*...*pow* pow*.....*smooth idle* "

most of this occurs at ~800 RPM. my timing isn't advanced or anything. I've checked wires, and the plugs, all normal looking to me. What's happening? Can your engine get used to 93 octane??

thanks in advance for any ideas.

 

Yeah its not a good idea to change your octane like that. I cant remember the scientific explination but basically like you said your car can get used to the 93 and then when you put the 89 in it will cause different things to happen like rough idle and hesitation.

 

yes but what is causing it? The recomended gas in the manual says 89 octane, so this still puzzles me.

 

the ECU has come accustomed to the 93 octane. give it a little while to figure things out and you'll be okay.

just make sure you haven't rewired your knock sensor too.. BIG no no.

 

oh ok. i thought there was something wrong with the engine. no my knock sensor isn't rewired

gas prices slowly going down in houston. $1.69 for 93 octane in my area. I'll fill the car up next week with 93 again. thanks for the input.

 

I'm assuming your car is a VG because you said the reccomended is 89. Just a quick note on octane levels. Putting 93 octane gas in a car that only requires 89 will in no way give you anything benificial. In fact because the 93 octane is designed to ignite at a higher temperature (for cars with higher compression or boost) it will actually produce less power in a car that is not designed for the higher octane.

If you want to stop spending money for gas your car does not need then I would suggest disconnecting your battery over night. This should cause your ECU to loose all of its data so the next time you go driving the car will relearn everything for the lower octane gas.

 

cars with knock sensors can still benefit from 93 octance even when 87 is recommended, and in fact a lot of manufacturers rate their engines on 93 octane and then recommend 87.. i know dodge has.

 

oh, and if you are a ve or vq, and like your pride, use 93 octane...

96 max se auto on 87 octane ran 16.7 consistently to my dodge dynasty's 16.2-4

 

hmm...thanks for that insight. Yes my car is a VG. I haven't been using 93 forever, mainly 89 unless the prices are right. But don't 93 octane burn cleaner than lower octane levels? I have a state emissions test coming up, and wonder if the 93 will help. So I thought several tanks will help clean up the emissions come test day.

 

As far as I know there is no difference in the "quality" of gas between the ratings. IE the 93 will not burn cleaner then 89, at least significantly. The refinerys have to put out gas that meets federal and state standards no matter what.

Stick with the 89 because if you switch to 93 a couple of days before your smog test your ecu will still be set to burning 89 and "could" cause problems because it hasn't reprogrammed for the different gas.

 

Wires and plugs OK. Did you take the dist cap off and check the rotor and cap. Look very closely for carbon tracks and burned contact points. When mine started diong this, the cap and rotor were shot.

 

Just stick with one octane rated gas and don't change back and forth. 93 for VE's or if your ride has advanced timing etc. Remember that higher octane ratings are for preventing knocking or pre-detination. If your car is not designed for 92+ don't waste your money.