Hi guys,

At first this problem only happened when the car was idling, however it has now started doing it under light throttle in heavy traffic, which does worry me.

When idling, AFR's will sometimes go way lean (up to 21, which is the highest my ZT-2 reads), rpm will drop to 3-400 rpm, and the car will struggle to idle for a few seconds, after which it seems to wake up and start fuelling properly again.

This week however, in bumper-to-bumper traffic on my way to school, AFR's would sometimes go to 21 even though I was giving the car light throttle and the engine was under load. This is what brought me to post here; running the engine that lean under (admittedly light) load surely isn't the best thing?

I logged the car on one of my drives to school, here is a pic of the log when the problem appeared. I'm not very familiar with STFT and how it should be reading normally, is it's behavior normal?

Link to full log:
https://spreadsheets.google.com/ccc?...thkey=CJTtiqUD



Thanks in advance!

 

Well for some reason your LTFT low and mid aren't working, that could be one cause... do you have your rear O2 disabled via periphery bits?

 

The car doesn't have a rear o2 sensor, so yes it's disabled.

 

Did it come with one? Have you done the rear O2 patch along with the O2 heater patch as well? I am thinking that your injector scaling/latency needs some work, but can't tell because your fuel trims aren't working...

 

Came with one but it was unhooked for the wideband. The injectors are stock so I don't see how the injector settings could be wrong?

I can post up the relevant tables if you want to take a look to make sure, just let me know which ones you want.

 

Here's another log where the idle goes from perfect, to "WTF!", then back to perfect. This time I also logged the o2 sensor

 

your front O2 sensor is most likely starting to fail.

 

Now that I think about it, that would make sense, because at one point I set up the car to idle in open loop and I don't think I had this problem. (Had other idle problems, but I also had a boost leka at that time). I'll put it back to open loop idling today and see how it goes. Open loop bypasses the front o2 sensor, right? so it should idle much better in open loop?

Also, I've re-enabled the periphery bit for the rear o2 and trims have started updating again. LTFT low is around 4% so far IIRC.

Finally, I recorded a little video of the tach and my ZT-2 display this morning, when I get home I'll upload it if the open loop idle doesn't fix the problem.

 

This.

Or your WB sensor is going out. How many miles on the WB?

 

The car has 41k, so less than that. However, it's mounted less than 16" from the turbo (It's on the vertical part of the downpipe before it goes horizontal), so that may have affected it's lifespan?

 

The other way you will know if the front O2 sensor is bad will be that you will not throw the CAT efficiency CEL if you are running a test pipe or hi-flow cat.

 

its funny my evos been doing something very similar... while its cruising its fine but only at idle it goes up to 17:1 afr often... before and after i installed universal o2, its always been like that. i chalked it up to my 272 cams and the crappy tune.

 

Yeah that def can affect lifespan. Sometimes when sensor go out on the ZT2, it just pegs lean.

Also, messing up the connectors can do the same thing.

 

My car does the exact same thing... idles around 18:1 or 19:1, then will drop to 15.8:1. It bounces all over. Also dies on cold start unless I tap the gas pedal a couple times. On SD, rear o2 disabled.

 

Alright, this morning in traffic running open loop idle: the idle still stumbles (3-400 rpm), but instead of going very lean, it goes very rich (10-11ish). When I pulled into my garage last night after work though I had to stay on the throttle to keep the car alive, otherwise rpm's were falling to 2-300 and I could hear a clicking coming from the front left area of the car, similar to when you finish reflashing the ECU and there's a clicking (coming from the battery I think?)

So, should I start by replacing the front o2 or the wideband?