Just bought a 04 A/T Ralliart a few weeks back. My main concern is my MPG.
I have read here that members CAN get around 30mpg.

If I drive 100% freeway on cruise control @ 65 mph the whole time, I only get 24mpg.

I have stock engine. New air filter and fresh oil change but unsure of the weight.
It does have 17 inch wheels which I know will lower mpg but not by much. No CEL.

Through searching the forums I have come up with possible problems/solutions to check.
-Clean MAF & TB.
-Replace Thermostat (How do I know if it is bad?)
-Use 5w30 Synthetic Oil (Since I do not know what was used)

Anything else I should check? Thanks.

May or may not be related:
Also want to add that about 5-10 seconds after I start my car and while I am idling in park, the RPMs will drop below 500 and almost seem like it will die for a couple of seconds, then I goes back to normal.

 

5W20 oil. Tire pressure about 36 psi cold.

 

I keep the pressure around 40psi

Is 5w20 on the thicker side? The oil in it now seems very light and liquidy.

Also want to add that about 5-10 seconds after I start my car and while I am idling in park, the RPMs will drop below 500 and almost seem like it will die for a couple of seconds, then I goes back to normal.

 

Is that 5W-20 a suggestion tailored for the canadian climate, or just in general?

 

o2 sensor and new plugs may help.

 

^This. How many miles on the car? Our plugs are good till either 90K or 105K. I forgot so someone correct me. Oxygen sensor can start to fail after 100K which can also hurt mpg. My car has 60K and I typiclaly get around 330-350 miles per tank.

 

cruise control won't give you the best mpg either...

 

Car has 126k. Which o2 sensor is responsible for A/F ratio?

Is there a way to test the sensor and plugs? or is it just replace-and-see-what-happens?



Thanks, will try without it. Was also just making the point that I am driving at constant speed, not passing people, and not driving aggressive.

 

The front o2 sensor. I have a brand new one sitting in my apt. I can sell it to you for cheap.

 

If the plugs haven't been replaced I would just do that as basic maintenance. You could do plugs first and see if that helps at all. Just replace the plugs with the OEM ones and you'll be good for another 100K.

 

If the thermostat is stuck open it takes the car a long time to reach operating thus it will run rich stuck closed car over heats.. Mine was stuck open but when I changed it didn't notice a big gain in mpg.. Looks like you should have your timing belt replaced soon if it hasn't been replaced yet.. Damn slc 330-350 I was happy getting 300 from 250 before.. I think I need a new a/f ratio sensor soon how much is cheap ralliartize it?

 

I do a lot of commuting. Average 27-28 mpg combined.

 

if i stay off the cruise, and out of boost, i still get pretty good MPG...i haven't kept track exactly...but i measure long drives from city to city, like from here to Ottawa is 286km or about 178 miles, and i got there on just over half a tank using cruise control and that was at 125km/h or 77mph, right on through 2 speed traps, they didn't care...anyways, that was with hackish's "shot in the dark" base turbo tune he sent me so i could safely drive the car to him...it was pretty rich under boost, but otherwise fuel economy did not really suffer...

@ crucialfix, can you get a scanner and get some data, like fuel trims and engine coolant temperature after a few minutes of driving...

 

The car is rated @ 23 mpg city - 29 mpg hwy which depending on your driving habits and vehicle conditions 24mpg for hwy still sounds reasonable. Those numbers are most of the time ideal numbers of the manufacturer and almost never you will obtain the same ones.

 

From the light, and the needle under E a little, I fill up with 10 gallons, and at that point I'll get maybe 225 miles a tank -_-