Hopefully this is the right section to post this.





I've got an NA S4 that I'm fairly new to (it's my first rotary). It came with an AEM wideband O2 and gauge, and they've been working quite well so far (AFRs make sense, in that when I'm cruising, it's 14.7, and when I'm on it, it's closer to 12).



Now, when I'm cruising, the AFRs will stay quite rich 12:1, then when I am at about 1/4~1/3 throttle, they go to 14.7 (as if I'm cruising, when I'm really lightly accelerating), then go back down towards 12:1 when I'm really on it. Driveability seems the same, as does idle.



Is there a common flaw that could be causing this? Is my TPS a likely culprit? It almost seems as if the ECU doesn't know when I'm at part throttle/cruise, and is confusing it with full throttle. What should I check?



Thanks!

 

Your ECU is not going closed loop when your cruising. AFRs will only be 14.7ish when the ECU

is closed loop. I can't remember all the inputs used but TPS is certainly one of them and worth

checking.



-Henrik

 

there is also that switch in the bottom of the radiator. its function is basically to turn on closed loop, and the emissions system. the switch doesnt usually go bad, the wires run under the battery tray and usually get kinked/bent twisted



another thing to look at might be the stock o2 sensor, if you still have it

 

On a side note, wow, I can't believe someone invested in a wideband for an S4 n/a!

 

I thought it was a bit overkill myself when I picked up the car, but if it helps me chase this problem down before it becomes a big deal, it might have been worth it!

 

easy to find, its on the bottom tank of the radiator, left side, BIG bolt lookin thing with 2 wires

 

Its not the sensor on the rad - if it was, it wouldn't go closed loop at higher throttle. Check

your TPS.



-Henrik

 

OK, so my initial hunch might be right... It was really stumping me how it's still entering closed loop mode at all, because I had assumed that a bad O2 or this other sensor would make it go to a default map with no ability to do closed loop.



I'll check TPS tomorrow, and see how it is.



Thanks!

 

Update:



Disconnected the TPS to check it's readings, reconnected it, now the car really doesn't do anything right.



Runs halfway OK until 1/3-1/2 throttle. At 1/2 throttle, air:fuel goes to 10.0:1, and the car bucks hard.



The TPS was indeed out of adjustment, and after the car started doing this, I adjusted it so that the car showed a reading of 1 volt. That didn't really help anything. Any ideas?