Engine lean at idle, rich on WOT

[solo_ryder]

Ever since I have done my swap I have been having some AF issues.. If I come to a light and idle it will start out fine then all of a sudden I feel a small shudder and the AFs drop to 16, 17 or leaner, then kind of fluctuate between 14-16 at idle.. Here is a video of idle even though its hard to see AFs with the flicker:

https://www.youtube.com/watch?v=345bnPHqYBg

Cold idle is fine (13s), its just the warm idle that is affected.

Under normal partial throttle driving it is fine and then under WOT it will almost always run 10.5 or richer in any gear. I turned the boost up abit from 7psi to 11ish and that seemed to lean it out slightly.

Why is this happening? I have also noticed that at WOT the boost levels will spike at 11 or 12 and then fluctuate between 8-11 psi, I know a spike then drop is normal but it doesnt hold boost it seems. Here is a video of a WOT run where you can see the boost fluctuate and the AFs:

https://www.youtube.com/watch?v=r_zRQ3dwt8Y

Car does not misfire at any rpm and plugs look normal. Car is parked for winter but would like to have this going well for next year. I am going to make a boost leak tester and see what that comes up with

Mods are:

Cone filter
VW OEM bypass valve (recirc)
Vibrant couplings with T clamps on every joint
s15 SMIC
3" downpipe
HF cat
3" cat back
Vibrant MBC
copper ngk 7's with a .38 gap

[blackmags91]

Yep, all that sounds about right..
Widebands are for tuning, otherwise they are for automotive hypochondriacs. Your car seems fine.

You could probably benefit from a proper dyno tuning session, but then again who wouldn't?
You'll know if your car isn't running right, you don't need a wideband AFR gauge to tell you that.


Car does not misfire at any rpm and plugs look normal.
So what the problem is? Mbn wish my sr was behaving that way.

Just my 2 cents. Good luck

[Tyler_240]

I think most folks run BKR7E's at around .028 to .034 gap. Other than that, it seems like its running fine, if it just started happening recently, remember cooler air temps will cause slightly higher boost, especially with the MBC.

[Croustibat]

you get high vacuum at idle ( => unmetered air ENTERS, runs lean), then another problem with high boost ( => metered air goes OUT, runs rich).

If it sounds like a boost leak and it tastes like a boost leak, then it probably IS a boost leak.

as far as your boost spike goes, it means your PID regulation has too much gain and not enough base set.


Anyway your boost leak is not an enormous one, engine makers always make their car run very rich on boost, to prevent the engine from blowing when they get a dying fuel pump or a kid adding boost without remapping ( mail order tunes are the same, just a bit less margin for error in fueling and ignition ).

[Driftwire]

Even on my Standalone tune I setup I tuned it and then richened it just a bit incase something fails on track or on street I have that safety net. Your car seems fine other then the lean spike at idle if you get a shudder. I also got that alot with my car but it turned out a slight leak at the BOV. Just check over all your hoses and piping. Other then that I wouldnt worry about it.