Inconsistent A/F ratios at idle

[LEMHEAD16]

After installing my M-300 i have noticed that sometimes my car idles at different AFRS. Sometimes it is in the 12-13 range sometimes 14-15 and sometimes in the 16-17 range. If I could get it to be consistent I could tune for it but I don't even know where to start? Any Ideas

[fiznat]

Your ECU will automatically richen up the fuel mixture if the engine (coolant) is cold- that could be making some of the difference.

Is your idle stable or does it wobble?

[LEMHEAD16]

it stumbles a little bit at idle. The ECU would explain the rich side but what about the lean side? Thanks Fiz

[fiznat]

Its not running lean really. If the engine is warm and you're at a nice low idle 700ish, I've seen idle AFRs reaching 18:1 with no problems whatsoever.

Do you have a FSM? I would check to make sure your coolant temp sensor is in spec, along with your TPS and MAF. If those check out and your idle is still wobbly, look for a vaccum leak after the throttle body. Unmetered air getting into the intake charge would cause the symptoms you described as well.

[LEMHEAD16]

I'll check the coolant temp sensor tonight

[nissanfanatic]

A lot of times.. if you let the car sit for a minute, it levels out to 14:1-15:1...