This a response on the ECU Tuning Forum; so I can't vouch for it's accuracy, but "OdinEidolon" is from Italy so I guess that's OK
He does run a Peugeot 406 btw
It does seem to confirm that readings between -2 and +2 are normal.
"Re: Fuel injector problems
Postby OdinEidolon » Mon Jul 23, 2012 10:55 pm
Hi there! There are very accurate sensors that measure the vibrations caused by the fuel exploding in the cylinders one at a time. Based on this and more data, the ECU calculates the correction to apply to every injector (4 injectors, 4 cylinders). The correction is calculated in mm^3/stroke, because it is the correction to the IQ - Injected quantity (called injected flow set point in that picture), that is the amount of fuel each injector squeezes in the combustion chamber at every cycle.
So if the |correction| is very big that means the injector has something bad, a value above 2 already is a hint, above 3 a proof, 4 is a certainty. Injectors should be removed (this can be a pain - I speak from experience) and cleaned professionally (with ultrasonic waves), or worn parts replaced. This is expensive. At least 60€/injector.
In your case if the corrections go to 0 at load that's a good thing. However it'd be nice to have a video of this during various stages of driving, that is as if you were driving normally. To do this grab a program that records the screen (like Autoscreenrecorder Free) and start it up, then go for a short trip.
Also specify if this happens from cold or hot more frequently, and if your revs go up and down..
My corrections too are very big (~4 numbers) just after I turn the engine on, then after a couple of seconds it settles down to ~1. Also strange, you have a very low idle. Mine idles at 750rpms without AC and 803 with AC on. I prefer a higher idle because the oil pump comes into play earlier, but that's not a huge difference. That can be changed via a remap by the way."