poor mileage, rough running, 97 lx-i

[bigskylxi]

Okay, i searched the forum, but can't find a definitive answer that i haven't tried. Maybe somebody can help...

The car:
87 lx-i, 194k, 5spd

What I've done:
brand new plugs, brand new o2 sensor (main), wires, rotor, cap, fuel and air filters all have ~6k on them

The problem:
Mileage has dropped from about 35 to 20, rough idle, rough running in general, pops slightly especially under deceleration load. basicially its running super rich. All this started about a month ago. Now, the odd thing is, when i reset the ecu after the new o2 sensor (which had been giving me a code) it ran almost perfect for about 20 miles, then it slowly deteriorated again. If i reset the ecu again, it will run pretty decent for another 20 or so miles. At this point i'm compleatly lost as to what is going on, no other codes were thrown. Any ideas?

[voiceinurhead05]

Vacum leak?

[shepherd79]

fix the ECU code.
if you are having O2 sensor problem, replace it with another one.

[bigskylxi]

I did replace the sensor, its brand new and everything is showing it working fine. The thing i don't understand is why it will work for a short time, then go super rich again. Would a vacum leak do that?

[shepherd79]

nope, the vacuum leak would make the idle go up.
you have a problem with O2 sensor.
when you reset ECU you reset the fuel and map curves in the computer, but after you drive for a while your computer will adjust them. try getting universal O2 sensor. they are cheap and all you have to do is wire up one wire.
another thing you can do is start checking all the sensors. may be one of them is not working properly and giving computer wrong readings.

[bigskylxi]

Well, i replaced the primary sensor with a universal bosch. Now, would the secondary sensor do the same thing? I thought that one was just a check for the computer on the primary sensor. I could be wrong though. The only code i was getting was for the primary sensor so....

[bigskylxi]

Also, with the new sensor no more codes have been thrown. so according to the ecu there isn't anything wrong...

[shepherd79]

you have 87 lxi,and 86-87 had 1 O2 sensor unless you have aftermarket headers or diff headers.

[bigskylxi]

ahh, good to know. I think i've narrowed it down to a definite sensor problem, which means either MAP or temp sensors are my current suspects as of right now. now, without the special little map connector how exactly do you test it? I'll search the board again, but if anyone has any little tricks that could help that would be great.