Houston, we officially have a problem.

[SuperchargedMR2]

Well I heard my daughter pull away from the house the other day & I noticed that the 94 Corolla that she has been driving sounded like it was missing a little. I looked around the engine bay, checked the plugs & they looked okay. I track the mileage & when I looked at the last few tanks the mpg dropped from 27-30 range to 21-22 mpg! Now the hassle to figure out what the heck is going on. It stumbles a little when driving it easy but when I get on it the stumble seems to go away or it's at least not as noticeable.

Any ideas on what to check are welcome.

[cipher93]

How old are the plug wires and distributor cap? Run some fuel system cleaner or dry gas like Lucas or Heet through it lately? Did she switch from conventional fuel to E10?

[SuperchargedMR2]

Originally Posted by CJRocker

How old are the plug wires and distributor cap? Run some fuel system cleaner or dry gas like Lucas or Heet through it lately? Did she switch from conventional fuel to E10?

The distributor cap, rotor & wires only have about 20k miles on them. I did put in a bottle of fuel system treatment too. I had them run the code & it ended up being a bad O2 sensor. I replced that & installed some fresh plugs & all is well now. She is running great again.

[Zain]

so bad o2 sensor can cause drop in fuel milege?
cos ive had a bad sensor for a while and i am still driving my car:P

[SuperchargedMR2]

Originally Posted by Zain

so bad o2 sensor can cause drop in fuel milege?
cos ive had a bad sensor for a while and i am still driving my car:P

Well it passed smog check about 5 months ago & mileage was okay until a few tanks ago. I just know that the check engine light came on & it has been coming on & off my daughter said. Changed it out & put new plugs in & it's running great again. I'll check the mileage after this tank.

[Bitter]

try to pull the blinky code. Does the car have EGR?

[REN69]

clogged cat, bad o2 sensor... could be anything related to the emmissions system.

[SuperchargedMR2]

Like I said, it was the O2 sensor from what the code was. A new O2 sensor was installed & the car is running great again & mpg are back up too.

[Zain]

Originally Posted by SuperchargedMR2

Like I said, it was the O2 sensor from what the code was. A new O2 sensor was installed & the car is running great again & mpg are back up too.

so i have to replace my O2 sensor
okey heres the thing my corolla originally had the screw in sensor, but then when my manifold cracked and i had to install after market headers. the header had 2 screws for the sensor so i bought an adapter to make my screw in sensor work with the after market headers.
so technically i can use both the screw and the 2 bolt sensor for my engine.

my question is which one is easier to install as i will be doing it my self?