Ive noticed recently (mostly after I installed my BC272s) that my car has been running very lean during idle. Like 15.5+ all the way till the wideband just does the little - - - thing. Cruising I sit somewhere between 11.7-12.8, once in a while ill see 13s. I just installed a clutch, so I havent been hard on the car. I mostly just drive from my house to work (8ish miles). During the drive is fine, but coming to a stop light or when I get to my destination the car runs lean as hell.. Could this just be a boost leak? Ive got a tacktrix cable on the way so once that gets here I can do a log at idle for you guys. Anything you guys can think of that might be going right over my head?

Being lean at idle is just fine. Mine is usually in the 17 and 18's at idle. My cruising AFR's are around 14 and 15.

There's really no reason for it to be richer at idle. All it's gonna do is use more fuel. There's not s load on the car at idle so theres nothing to worry about.

banshee04 said:

Being lean at idle is just fine. Mine is usually in the 17 and 18's at idle. My cruising AFR's are around 14 and 15.

There's really no reason for it to be richer at idle. All it's gonna do is use more fuel. There's not s load on the car at idle so theres nothing to worry about.

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Wow.. Guess I never even thought of it like that.

Check your front O2 sensor. At CRUISE (constant speed) you should be seeing 14.7:1, same as at idle. Sounds like you're stuck in open loop at cruise which would make you run like you were on the throttle constantly. Was the car at operating temperature? Got a log yet?

Idling lean may or may not be "fine" for the engine but it's certainly indicative of something being broken.

I remember reading somewhere on these forums that if your car Idles very lean the ECU's internal capacitors maybe starting to leak. You would have to remove the ECU from the car, open it up and check the "caps" out. If they are leaking you will have to send the ECU out to ECM Link for service. I hope this helps, Corey

Absit said:

Check your front O2 sensor. At CRUISE (constant speed) you should be seeing 14.7:1, same as at idle. Sounds like you're stuck in open loop at cruise which would make you run like you were on the throttle constantly. Was the car at operating temperature? Got a log yet?

Idling lean may or may not be "fine" for the engine but it's certainly indicative of something being broken.

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No logs yet, I mentioned in my first post that my tacktrix cable was on its way. Until that gets here I have no way to do a log. Ill definitely look into the front o2 sensor though.

Did you ever fix this issue? mine has the same issue and i tried to richen it down a bit but nothin.

Whoa! I actually forgot about this. A couple months after I started this thread I moved from California to Wisconsin and started using a buddys DSMlink. Since then Ive never noticed this issue.

A pre WB sensor exhaust leak could cause you to be reading slightly lean at idle.