Rough idle and lean AFR!
 

Hello all...
So I have been searching forums and doing some work to try and figure out an issue that just popped up and would love some help or ideas as to solutions,

As of recently my startup on my evo IX is incredibly rough like it almost stalls out before it finally warms up, while it's basically choking on startup the AFR will bounce all around to keep it alive, once it has warmed enough my AFR will sit anywhere between 15.5-17 while not moving and at warm idle, it was NEVER like this. While cruising it is perfectly fine easy throttle around 14-15 AFR and at WOT it's very low around 10.5-11 AFR. car drives fine and it does not fall on it's face but I am trying to get the AFR back to normal at idle..
mods include TBE, LICP, walbro 255, HKS 262 cams, manual boost controller

I have:
cleaned the MAF
did a boost leak down test to look for any leaks
checked for exhaust leaks
replaced timing belt (yesterday not for this reason but it eliminates timing issue)
fuel pump kicks on and I do not have a shortage when driving so it's not that

I'm just looking for suggestions on what it could be or what to check next, any help is highly appreciated!

Check the fuel pressure with a gauge.


You 're not supposed to clean the MAF on these because it's not a MAF.

It's a Karman vortex volume air flow meter.
Trying to clean them ends up breaking them.

FWIW, countless evo owners have been using CRC MAF cleaner for years and years without issue, Just don't concentrate the spry directly on the thin wire of the resistor, have some common sense, We all know what the label says but when used correctly it works just fine and will not harm or break your MAF sensor in anyway.

I have never heard of one single person breaking or damaging a MAF using CRC's Product, Hell I remember a dude used break cleaner with no ill effects, I wouldn't suggest that But I personally used the MAF cleaner for well over 100k with no issue to speak of. Works great.

They don't get dirty in the first place so there's no point in trying to clean something that doesn't need cleaning.

The only people who try to clean them are the people who don't know wtf they're doing.


As for what to do next.....check for stored fault codes and get a data log.

you can check if it is maf related by unplugging the maf and letting the car idle like that..

doing a datalog will tell you if the water and air temp sensors work, but I would ideally like to see what the lambda does... maybe you can unplug the o2 sensor and see if it stabilises... sometimes when the o2 sensor goes bad you get these weird idle issues..

No you can't.

It doesn't work like that.

When you unflug the AFM it runs in limp mode, as in alpha N mode where it's controlled by the TPS instead of the AFM.

Update
 

Okay I really really appreciate everyone's input and I'd just putting an update here, so Just so happens that my SES light is out hmm how weird definitely couldn't have been the used dealer I bought it from... regardless I am running P0011 for my variable valve timing which could be a lot of things, exchaust leak, bad cam actuator, bad cam position sensor, bad tune, or nothing at all and just because I have upgraded cams... regardless now I'm back to square one with a slightly new clue on solving this issue, also the car now feels sluggish under WOT, I do not even know where to start in terms of trouble shooting now..

Murphy's law says that the problem is to do with the last job on it that you did.

So that's what you check first.

There's always more than just one problem, because there's more than one mod.

Can someone corroborate this?

I've had to clean mine before. I've never heard anyone say this.

That guy pops into various threads with ideas nobody agrees with. It's odd.

Anyway, OP: This is a long shot, but those are usually the ones that fool us the longest: my problem was a bad alternator. It wouldn't supply enough power to charge the battery and/or run the car. I would run lean at idle. I didn't catch it until it started doing the same while cruising on the freeway (about two years later).
I bought a tester from Harbor Freight for $10 and found my problem. 'Thought I'd mention it, just in case.

If your alternator is bad, it won't run lean.

But if your alternator is bad AND it's tuned wrong, then it might.

Probably because I've been playing with turbos since long before you were ever thought of.

Crazy that it runs fine after installing a new alternator, though. Guess I got lucky.

must be it. Jesus, how old are you?

:lol::lol:

you sure spew out a lot of bad advice which is not a surprise considering you do not work on evo's...