I had my '03 HCH v1 in for a relatively comprehensive service check a couple of mos back. I was told by my dealer's service dept my engine needed air induction service done to improve my milage. Unfortunately my milage went from low 40's pre-service to 38ish post-service (and that's after alot of effort in driving frugally). That's not supposed to happen, right? Could they have done something wrong? I also got new tires during that service call; would improperly inflated tires impose that much of a penalty???

dont know much about the 03s.

A couple of things.

If you have new tires, they may have higer rolling resistance than the old ones. You might want to see if they can be pumped up towards the max sidewall pressure - 40psi or so would be a good start.

Perhaps you are now driving in colder temps than before, which will drag down FE. In my HCH2, every 4F drop in temp lowers my FE by about 1 mpg.

Yeah. It's probably the cold temps. I would wait till spring (actually I'm not that patient, so I would drive to Arizona or somewhere hot)

Getting new tires sucks. It kills MPG unless you get a specifically low rolling resistance tire. I got new michelins to replace my stock dunlops at 60k and dropped about 10% for about 5k miles then it evened out to about a 5% drop on average.