How much should a Wideband reading fluctuate at idle

Installed an AEM Wideband over the weekend and thought the readings would be fairly steady, but it seems to bounce around at idle between 13.5 - 15.9. Is this normal?

No I wouldn't say that's normal, however it does depend on your engine's mechanical modifications. For example with an aggressive cam that has a lot of overlap you're likely to see the AFR move around more than a stock unmodified engine - I still wouldn't expect to see a variation oas large as you're seeing though. A misfire at idle will also cause erratic AFR readings.

In most cases I'd expect to see my AFR at a constant idle be within +/- 0.1 to give you some idea of what could be considered normal.

Ok. thanks Andre I didn't think so either. It's a stand alone unit and I figured it would be more inline from what I'm seeing from my tuning software...at least at idle. No misfires to speak of. I do have a mild cam, but nothing too wild.

What injectors are you using and what engine is it?

Injectors are stock ford 19lb. Engine is a small block ford 306 cu in with a Ford E303 cam, liberty aluminum heads and 76mm MAF.