RB25 Rough Idle/Lean Condition - Help Please

[ocelotmother]

I have been battling this thing for the past couple months now, and figured I'd finally get on the forums and see if someone with more knowledge can provide some help or insight with the matter.

The issue I'm having is very similar to a vacuum leak situation. It is running lean, the idle is rough/engine shakes (idles at 600-700 after warm up, seems to die when not given some throttle before warm up), and it hesitates and bogs when holding throttle at any rpm for longer then a second or two. One thing to note is if I let everything cool down overnight and go to start it up after letting it sit for a long while, it fires up perfect and revs as it should and just runs properly for the first 5-10 seconds. Then it's as if a switch is hit and it just starts running like crap again.

My AFR at first start up is around 11-12, then as it starts to run worse, it gradually decreases all the way off the scale, past 22 on the gauge. If I blip the throttle my AFR jump to more proper level, around 12-14 area. While revving up and holding throttle down at a certain RPM level, the AFR hits around 12-14 area first and then gets really lean right after (I believe it goes all the way past 19-20 if not more).

A lot of the symptoms point at a vacuum leak, but I do not hear any major hissing sounds, and I have checked all the lines and clamps that I know. The only issue I am aware of are a few exhaust side leaks which I will be rectifying this coming week. I have a leak between exhaust manifold and turbo, as well as the turbo outlet flange and downpipe (pre O2). Weird thing is, I would think a leak before O2 sensor would cause a rich conditions as opposed to a lean one, and that's what is boggling me.


From the top of my head, I have done the following so far:
-replaced the fuel pump
-got brand new and tested injectors
-a new engine wiring harness to cross out any potential wiring issues
-checked FPR (without vacuum fuel pressure is around 43 on gauge)
-me and my friend used a fog machine to check leaks (it was a crappy one and will try to fog it again with something better), did not find anything but a small vacuum leak on the throttle body which we fixed
-used seafoam, added to vacuum line to check for leaks, found the turbo inlet and outlet gasket leaks + wastegate v-band slightly
-replaced old MAF with new one from ISR
-replaced spark plugs (gapped to 0.28)
-checked coilpacks
-replaced O2 sensor
-checked TPS voltage (~0.45v at idle)
-played with IACV, was also cleaned out around 5 months ago


Rough Parts List Involved:
-Z32 MAF
-HX35
-Front facing manifold
-Catch can
-LS2 coils
-550cc injectors
-44mm wg
-q45 throttle
-adjustable fpr
-electronic boost controller
-fmic
-walbro 255 fuel pump

Last time it ran somewhat decently was right before my old ECU got water damage and died. I then got a new one from RS Enthalpy and upgraded the injectors, and just never got it to run properly since I put it all in. I know logic would say it's a tune issue, which it may very well be, but I also think that this new tune might be "less forgiving" to any engine issues I may have had and have since my last one. If that makes any sense lol.. I will also contact Martin at RS Enthalpy on the matter however.

I will check voltages on all sensors next chance I get and post them up. Aside from the O2 sensor reading being off, I don't know where else to look. I don't understand how just an exhaust leak would cause a lean condition. I'd appreciate any kind of help or opinions on this matter ladies and gentlemen. Thanks in advance!

[ocelotmother]

I also forgot to mention, I do have DataScan on this car and took a couple logs. First I made a log of just idle, then I took another log of some revs. I don't know if this would help at all. Also, another thing I did not mention is my catch can set up. I didn't have issues with it before but at least worth noting. The catch can has two ports. I got one port hooked up to vacuum line on intake, and the other port goes to the exhaust valve cover. I think that is the correct way to set it up if I'm not mistaken. But there don't seem to be any leaks in that system. No major ones at least.

Anyway, I was not able to attach the log files, so I have them uploaded to my google drive instead. You should be able to replay the log in datascan 1.

Idle log:
https://drive.google.com/open?id=1SN...QitkQOpXBt2Znu

Rev log:
https://drive.google.com/open?id=1q7...TfV1--YgvwMkd5

[nisileighty]

Check your cam angle sensor timing.

[ocelotmother]

I did play around with it, but I'll give it another look! Thanks for your suggestion mate!

[dalecl9]

Any update? im having a similar issue.

[ocelotmother]

Long story short, it seemed to have been the tune. I got it retuned and it ran much better. I dont know what it was exactly though!