fine members I need some help, I have recently purchased a 2010 Corolla, have less than 5K on it and am finding that i am getting terrible fuel economy, 400km per tank 420km max.

i am not a lead foot, my drive to work is all highway, don't do much in city driving.

I have a 2.4L engin on the XRS model, automatic. My buddy told me that the computer might be in emergency mode or something, any ideas on what I should do?

   

Check the throttle.............it may be sticking.

   

did u seat the rings properly ?

   

I'm thinking a trip to the dealer for a warranty inspection is in order. The problem can be any of a number of things; the mass air flow valve may be stuck or blocked, it may be a software error, the fuel injection air-to-fuel ratio is wrong, you may have a bad/dirty air filter (you can check that on your own), the inflation in your tires may be low, you may also have the wrong size tires on your car for the software settings (this happens - check the VIN with a 3rd party tire outfit to see what size tire is correct for your car), the spark plug wires might not be installed in the correct order, and etc.

But where it is a new car, this is a problem for your dealer.

   

mmm, i have 15" for snow tires on, usually 17", could that be the problem?

   

It can be. If your car is designed to cruise at 120Kph with a specific diameter tire and then you run a different diameter tire you will raise or lower your optimum speed.

My Volvo S80, for instance, came stock with 18" rims and 245/40/r18 tires. If I put the 15" rims on with basic tires I will change the diameter of the tire by almost 2" and the 'cruising speed' of 70mph will effectively be reset to around 62mph.

   

Often the tire dealer will go -1 on the wheel size when installing snow tires. But if he knows what hes doing, that is compensated by the tires having a higher aspect ratio (ie sidewall) it give almost identical tire diameter. Going -2, as in your case seems a bit strange. Was this your idea?

But still, I don't think your car's computer takes engine management info from your tires. A smaller tire diameter might screw up your ABS working properly tho. Also you speedo would be way out - reading a lot higher that you're actually travelling.

   

yeah it was my buddies idea, he is a mechanic and told me that all i need is 15"s, i'll be sure to tell him he owes me gas money

   

So your speedometer could be totally inaccurate and you're revving way too high to keep up with traffic flow. No wonder.

http://www.1010tires.com/tiresizecalculator.asp

Input your summer tire specs and winter tire specs and see the difference.

   

thanks for all the input!!

   

   

Try measure your speed with a GPS against your speedo