It's seemingly getting worse over time, but my afr's on my Evo are bugging me at idle. It used to hover around 14.8-15.2, but now it jumps from about 14.2 to 15.5. Car doesn't sound any different or run any different other than this crazy lag I've had lately. I'm not sure if that's normal (car has a 2.3L, 35R and a bunch of other mods on the stock ECU), but I figured I'd try to find out.

I thought it might be an exhaust leak, but had that checked and it seemed to check out ok. If it's the wideband giving up the ghost then that's ok, but I just want to see if that's a normal operating range.

 

idle is going to swing rich to lean, no way around that. check your LOW fuel trims to see if they are within +/- 10%

 

I would start by installing a new wideband O2 sensor.

 

Boost leak test. Clean throttle body. Make sure fuel trims low are +\-5%

Probably nothing to worry about.