I have a 05 XA Manual Shift all preventive maintenance is performed always. but recently In the last two gas fill ups I was down 85 miles from my average miles per tank. This last tank I'm 45 miles down I have not changed any driving habits or anything i have just hit 115K mile mark but i do have all new Spark plugs, upper engine has been cleaned of carbon, the oil has been cleaned and the fuel system has had it service and been cleaned in the last 2 thousand miles so im not sure whats going on i have no Check engine light on and i checked computer for codes and none are stored...

So Im Confused on what's going on...

Please thank you so much.

 

That could be a host of things. You said preventative maintenance has been done so I assume you have a new air filter and you said you have new spark plugs, so I would look at (listed as most probable and least severe first):
1. Check your gas cap tightness and gasget material

2. Check all air hoses (ie. intake hose, hoses from the valve cover, etc.)

3. Throttle Body probably needs to be cleaned (@ 100k this isn't a bad idea anyway)

4. Your MAF sensor might need to be cleaned or is going bad

5. 02 sensor might be going bad

6. ECU might need to be reset

Just somewhere to start anyway. Generally it will be something in 1-3. Hope this helps.