Lean at Idle code, barely idling

RESOLUTION: PCV valve hose had fallen off. Check your hoses.

I was at an autocross on Saturday, long story short at the end of my second run I came into the paddock and had a really rough Idle, jumping up to 1000rpm and then down to 400. AFRs going super lean at 20+ and boost vacuum is only hitting -6psi ish. Happens cold and warm, no change.

No oil or fluid leakage, no abnormal mechanical sounds in the engine bay.

Datalog is attached, something to note is the car runs better when I give it a little gas, AFRs richen up etc.

Looking for advice on where to start troubleshooting; one of the theories thrown around in the parking lot is that there is a pre-O2 leak at the downpipe to turbo connection, as it is missing a stud, and maybe the gasket finally gave out with the thrashing it got on Thursday?

Hoping to have time to run down and grab my old boost leak tester this week, but also looking for things to check today during my downtime at work.

 

FMIC or TMIC? Similar thing happened to me on the way home from Indy. I didn’t securely fasten the coupler on one side of the FMIC and it popped loose.


Sent from my iPhone using Tapatalk

 

TMIC, but the couplers look totally good. Were your AFRs similarly lean?

 

I don’t remember, but lack of boost and lean AFRs is a pretty clear indication that something post turbo is completely disconnected or has a gaping hole in it.


Sent from my iPhone using Tapatalk

 

Encouraging! I'll try to get a good boost leak test in this evening, maybe something can be found.

 

So I found what I hope is the culprit - the nipple coming off of the turbo inlet pipe from the boost control solenoid appears to be cracking at the base, leaking out air almost at will, essentially allowing no pressure to build in the system at all. Pic attached.

I JB-welded the balls off of it, hopefully that can sustain it until I upgrade next month. Will be pressure testing the system again this evening after I am certain it has set properly.

Hopefully that would explain the lack of vacuum pulled to the turbo, really lean AFRs, and stumbling idle?

 

Still having issues - pressure test is good, but the behavior and data off the AP is reading exactly the same.

 

Wiggle the MAF wiring gently while it idles. If the engine changes behavior, you've got some wiring to do.

 

What turbo and EBCS are you using? I had to cap off the restricted port on the turbo but later on the rubber vacuum cap had cracked. It caused lean afrs and rough idle.

 

Do you happen to have a catch can setup?

 

Will do.

Running stock turbo stock EBCS. I was thinking it might be the EBCS, but I'm not sure how to test that.

Dual Catch can setup off a Damond PCV plate. PCV Valve -> closed -> IM, and two lines from the plate ports to a vented can.

 

Have you checked your lines to the catch cans? If not maybe one of them is bad somehow?

 

Haven't had a chance today, but the preliminary check, they should be totally fine, lines are brand new from Damond and are tight on their fittings. I will give it a more in depth look tomorrow and report back.

 

“Brand new” is just code words for “not properly secured” where I come from lol


Sent from my iPhone using Tapatalk

 

You are 100% right. The hose to the PCV valve had fallen off, ergo unmetered air being pulled in via the Intake Manifold. I am guessing since there is a check valve going into the Intake Manifold, I wasn't hearing anything leaking from that hose, and I apparently wasn't raising the crankcase pressure high enough to open the PCV valve and hear it from that vent either in my boost leak test. Took a more solid tug to see that it had come free.

Either way, spent all day taking off and putting on the Intake Manifold, all in all a good Sunday.

 

Glad to help man. Let us know how it is doing now and what numbers you're getting now for vacuum and all that

 

Running like a champ now, vac is reading -10 +/- 1 like normal. AFRs are clean. I should really just create my own build thread so I don't clog up the forums.

 

I agree but good troubleshooting thread for someone who could very well have the same problem.

 

what is normal boost vacuum supposed to idle around? lately mines been fluctuating from -8.4ish to -7.8ish at idle and also getting p02187. Also notice a crack on the downpipe pre o2 sensor would this lead to both the p02187 and low vacuum issue ? or should i be looking into injectors ?

 

If you have a crack in the downpipe you should fix that before doing any additional troubleshooting