Engine loosing power and gas mileage.... solution?

loosing power and gas mileage.... solution?

I am loosing lots of power and gas mileage. The thing is the gas mileage in the city is normal but the highway mileage is about the same as the city mileage. I have been getting kinda a rough idle. What I dont get is why I could have a decrease in power but also have a decrease in gas mileage. It doesnt make any sense. The compression is normal actually its about 10psi higher than normal in all cylinders. The vacuum pressure is at 17. The only thing I can think of is I might need need spark plugs.... oh also I noticed that the tips of the plugs are whitish... could that mean anything? I even tried using fuel injector cleaner twice. And something else I noticed is that when I am going 70mpg on the highway and then let go of the gas the car slows down a lot quicker than normal. Im thinking maybe the tires might have too much friction. I know that the brakes arent too tight. And the tires have the correct amount of pressure.

could it possibly be the oxygen sensors? Although I dont have the cel light on and Im not getting any black smock... or blue smoke for that matter.

have u tried resetting ur ecu?

how many miles does it have on it, i doubt the trd muffler had anything to do with engine wear, if anything that probably improved your engines life span

my mistake by any chance is your car a silver 2003 corolla. theres no way that you could have worn your engine down in a matter of a little less than two years. you wont see stuff breaking untill like 50k or 60k and those are cars that are abused daily. did you check your belts? maybe thats why it has a rough idol?

Umm... A LOT, a lot?

I would think it could be an 02 sensor too, but it should have set a code and turned on the check engine light. Sometimes they don't aways turn on the light.

yea i tried that..... also im noticing that when it is at idle the rpm needle goes up and down very slightly though. I wonder if I maybe wore down the engine when I had the trd muffler on and did a lot of engine redlining.

btw.... its actually a 98 corolla im talking about..... i have a 03 and a 98 lol.... it could be the o2 sensors (no check engine light on like i said). Im just wondering about how to check them though. Another cuprit I was thinking of is possibly there might be a gasget leak over by where the intake manifold hooks up to the engine. Im going to check both the manifold and the o2 sensors.

change the spark plugs and the wires, maybe you are not getting enough of a combustion in it.

ya know what i kinda have something like that im losing gas like crazy, i can watch it go down in a week, but i might just be driving more... or something