The CEL came on after running about 150 miles on a 93 octane tune with 91 octane fuel. I don't know if it is related...but I don't know that its not. The car is running fine, I haven't noticed any differences at all.

Heres the codes:
P0171 System too Lean (Bank 1)
P1131 Lack of Upstream Heated Oxygen Sensor Switch - Sensor Indicates Lean - Bank No. 1
P1151 Lack of Upstream Heated Oxygen Sensor Switch - Sensor Indicates Lean - Bank No. 2

The car has gears, 2/3 exhaust with o/r X, JLT RAI and custom professional tune.

 

are they coming back or just popped on once? I would not worry a ton if its just a one time thing...

 

The light just came on once during a cruise...I haven't cleared them yet. I'm not super worried about it.

 

I'm willing to bet it is just a freak occurance that happened to happen when you had the 91 in the tank. Every once in a ahwhile my car would pop the CEL on with the o/r X before I got the rear o2s shut off, it would always have some strange code that made no since.

 

I'd tend to agree. I just wanted to be sure, especially if I end up selling the car in the next few weeks, I don't want to screw anyone over.

 

[&o]

Well...I haven't been driving the car much at all. It was three weeks or more after the time that I posted this before I drove again, another month or so before I cleared the codes. I've driven it probably 50-60 miles since. The codes came back today...and I know it has good gas in it now, so that is out.

I guess I really do have something happenin'...

 

Clean your maf.

 

Have you been messing with egr or plenum lately, egr flow might effect downstream oxygen sensor, or exhaust leaks?

 

Not a bad idea, will do.

No, the only thing I've changed in the past few hundred miles was putting on a JLT RAI. I suppose it could be related, but I'd expect any vacuum leak would also cause rough or uneven idle. I don't think I have an exhaust leak, but that is another possibility.