Thats normal. almost all the fuel guages (atleast the ones in local cars) show just an average figure.if u see how the fuel measuring system works (HowStuffWorks - Learn How Everything Works!) , u ll know why is that so. So, all the real time info that u get in ur dashboard screen is average, not accurate. infact i dont believe those figures at all... and the fuel measuring system of new city is even stranger. im not sure but this is what a friend (own of city) told me. we both were in his car, he has cng in it, the fuel guages showed a completely empty tank.i said get some petrol, he said i ve got half tank in it, atleast. he said that city has some sensor in the fuel pipe, it calculates how much fuel is poured in when u get a refill (at refills, his needle DOES show the petrol, but not after that) and it lifts the needle according to that.
after that, it drops the needle NOT by measuring the remaining fuel in the tank BUT by the fuel consumption being shown on the screen. (thats y his needle showed zero fuel cuz it wasnt buring any petrol). now, i dont know if this is gud or bad, but i think this wudnt be accurate, but let me say im not sure here.
as for ur other question of RPM, once again, the same guy as above told me that when parked or in neutral, the ivtec engine wont rev more then 4500rpm.it has a limiter in it to keep the engine frm getting useless strain by high revving for no gud reasons.it basically cuts fuel supply to engine when touched 4500. it only revs complete when being driven. now this system, may be annoying for a few people but i wud say its great, why do u need to rev that much in neutral after all?
i guess ur confusions r cleared now. if not , im sure experts wud be around here soon 
