I have a 1999 isuzu rodeo with a 3.2 engine it has a loud air noise
when cold coming from the air cleaner box it idles upto around 1500rpms
while it is making this noise then after a minute or so it stops
completely and returns to around 700 or 800 rpms normal but still runs
perfect but seems to assume alot of gas please help please

 

it sounds like the fast idle is making the engine run at a higher RPM...it doesnt sound like a serious issue to me,but if something has changed recently, i would suggest a shop.