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Discussion Starter · #1 ·
ok, so i have an 89 na, and i am pretty sure that my 4 wire O2 sensor is bad.

anyways, when the engine is cold and i drive it, the engine stumbles under 4000 rpms, unless i push the gas pedal farther than 2/3 down. after 4k rpms or almost WOT, it runs fine.

now my question is, what exactly does the ECU do to make the car run this way, i mean, if i am just cruising around town, say.... 3rd gear doing 30mph, and i slowly roll on the gas, the car doesnt accelerate, it just starts stumbling. why?

does it run lean when this happens, or rich? or does it just retard the timing? i am looking for a somewhat detailed explanation of why a bad O2 sensor makes this my engine fall on its face? and why it accelerates normally under WOT or over 4k rpms.

any help is appreciated
 

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lean wont run bad like a rich condition. im not sure, but i think there is a different fuel map at WOT, not sure though.
 

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Errr...lean WILL run bad. That's what happens on my over-sized pulley J-spec GZE under 3000 rpms if I were to stomp on it. It wants to stumble...

Yes, there are two different modes that are used for WOT and not... Under WOT, the ECU pretty much runs the car rich, rich, rich, without regard to the O2 sensors.

I'm still not smart enough to answer this to the level you probably want, but just wanted to give a little more relevant info than has been offered thus far.
 

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A bad throttle position sensor will act like this also. Mine did. I had an 87 na. It would run for a little while then stumble if i held the throttle down it would stumble to about 3500-4000 then run fine.

I am not saying a o2 isnt the culprit but might want to check the TPS also.
 

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Discussion Starter · #5 ·
thanks 8, and thank you bmerton.

whats funny is when its warmed up, it runs fine.

i guess th TPS could be okay, but its funny that it's fine now, but wasn't when i bought the car. i havent fooked with the TPS..........
 

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Im not sure this applies to the 4A but if it runs fine when warmed up, you might check your IAC valve. If the 4a has one that is!
 

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yes the 4a has an IAC (idle air control) valve. a bad O2 sensor will not cause it to run like dookie. i would check the IAC and the TPS it sounds like maybe alittle of both.
 
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