This has been occuring for the last couple fill-ups, but ive been getting HORRIBLE mileage, and the car stays in open loop (o2 voltage not cycling) even while cruising.

Bad o2 sensor? map sensor on the fritz? ideas?

Hey I just had sorta the same thing. Mine was the opposite though. It was always in closed loop. It even cycled at WOT. I used $13 in gas just driving less than 2 hrs. and the car ran like complete crap. Anyways I replaced the 02 sensor and now it runs perfect. Mine was covered in black soot and having 73K original miles on it didn't help I guess :/

which O2 sensor did you replace? Just the one in your downpipe?

Wondering if it is ever necessary to replace the one in my catback?

I have noticed the same of my car, how it has been in open loop for a while, and then goes back to normal. I don't remember the site i saw this little trick at but i was thinking it may be worth a shot if it stops the o2 sensor from sending any negitive signal back to the computer, and that was using the 1/4 watt 1megaohm resistor and putting it inline with the sending wire on your sensor.

Have you noticed a spudder out of your car at WOT, or even just off the line at a slow pace? Mine has been doing that for a couple hundred miles or so :( .

no studder, car drives fine at WOT. only driveabilty probs are sluggishness sometimes as its driving in open loop during normal driving (too much fuel) and it died today when i left the car on idling to warmup before i left for work. other than that and the horrible gas mileage, its fine :/ :(

Mine ran ok at WOT also. But it'd die at stop lights and have hardly any throttle response. I had to rev the crap out of it just to take off in first. And when I did take off I smothered everyone behind me in black smoke.

somehting new, dont know if this is even related tho?
http://www.2gnt.com/dcforum/DCForumID16/4049.html