My Parents had a 2012 Fiat 500 TwinAir, lighter car than the Panda 4x4 and a few years ago so there'll be differences, but it was the same basic engine in 85bhp form. That seemed to perk up considerably over the first 10,000 miles. By 10k it responded the same in 'Eco' mode as it did in non-eco mode when we picked it up brand new, so it loosened up considerably.
We got mid-late 40s to the gallon overall, but weren't trying at all and it got driven at low speeds quite a lot. On the open road we managed mid 50's pretty easily, but I'd expect the figures for Panda 4x4s to be reduced a little due to the 4x4 running gear & associated weight. Brilliant engine, we still look back fondly on it, some 4 years after selling it.