running a little lean..

[evolution23]

94 gts-25t

EDIT:

well.. parked the car the other day so i decided i would take my valve covers off and check everything out see whats up and i find this..




the 100xxx km servicing was just done 2,000 km's ago. im assuming this has been my lean idle issue? rubbing against the back plate messing with my timing at idle but under boost there was enough power that it rubbing didnt make a difference?

Another EDIT:

pulled it all apart now, tensioner looked like it was cocked sideways a bit but it was hard to say. anyways took both the idler and tensioner off, made sure i put them on properly and nicely, swapped on my old belt that i think has 8k on it (hopefully) then spun it around twice by hand with the tensioner backed off, then tightened it and spun it twice again and the belt seems to stay in place but i guess we will just see. going to re-assemble and run without the timing cover to make sure it isnt wandering anymore and hopefully it idles normal again!

[evolution23]

anyone got 2 cents they could share..? any ideas? as its most likely something extremely simple and free to fix so id rather go that route then waste money having a shop run pressure test, etc..

[Fred-R]

IMO, the important is on load: if your afr' ok while boosting=no problem. 14-15 while cruisin is a lil high, your right (anybody has somethin to say bout 14-15 on cruise?)

[evolution23]

yeah under load it seems fine. still hitting high 10's under full boost (stock ecu, same numbers as before) but while idling and just cruising it seems to be in 15's most of the time. instead of being in 14's 90% of the time and hitting 15's a little bit, its the opposite now. i tried wiggling all hoses to try and get a slight change and cant get anything. thinking maybe i timed the CAS a tiny bit off? or the tps/throttle body something isnt quite right there after removing it?

been looking into this a little more online and iv been reading that at idle under 16 is fine. i thought running lean at any time was bad? under boost its the same and fine, but idle and cruise to me seems a bit off since its a bit higher and i dont think its fine to run even a little lean at any time. maybe someone can enlighten me if my numbers seem fine?

[h4X6]

No... lean under boost is bad... mildly lean during cruise or idle I think is OK


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[evolution23]

hmm. well this morning when i started the car up it was a little chilly still and it was in 15's/16's. then now when i started up the car (after it baking in the sun all day) it was reading almost normal. not really sure what to look for now. i think ill clean the maf, go over all the vacuum lines and intake, adjust the fpr again back to specs and see what happens. probably nothing but i am clueless

[h4X6]

I would say after checking all that and its still doing it then leave her be.... if you fine under boost then no worries.



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[Skym]

If haven't changed gasket, throttlebody leak. If used carb cleaner, could have got some on seals and damaged seals on throttlebody butterfly shaft (airleak). Or haven't tightened intake hose clamps enough or seated intake hose joiner correctly.

But a BOV vented to atmosphere with diaphram could cause similar symptoms (diaphram is affected when it's hot, cold), especially with the copy BOV's (known to leak) and could be leaking at idle. Once on boost, pressure helps to keep BOV closed and probably why it disappears. That's one of the reason's behind why I run a non diaphram BOV (Synapse).

[evolution23]

pretty sure its an intake leak and my best guess was at the throttle body as well. i am running hks ssqv bov but never had issues with it before the engine work so im assuming its fine since it was only removed then put back on the j-pipe with new gasket maker. tomorrow or possibly tonight im going to check over the intake pipes i removed to make sure i put them all back nicely then probably loosen off throttle body bolts and tighten them down in like a "kitty corner" way again so it goes on nice and even and just see what happens. pretty sure thats all it is was just concerned that replacing all those parts i might of done something wrong.

[h4X6]

That doesn't make sense. If it was an intake leak then you would see it leaning out under boost too but that's not the case.


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[Skym]

It's just to eliminate intake leaks as a cause (it might not be the cause).

Going by your description and that you changed coolant, etc, coolant temp sensor for ECU if engine was lean when cold. Sometimes gunk sticks on coolant temp sensor itself, causes problems. Check the coolant temp sensor when the problem happens and match against factory voltage vs coolant temp figures.

[evolution23]

intake is good, throttle bodys mounted nicely, timings spot on, fuel pressure is correct as well.. so it leaves me with.. exhaust leak?

there is a chance it could be a leak on one of my downpipe gaskets. shop removed the downpipe when they did the clutch, the test pipe had brand new gaskets (like a foam gasket) and down pipe would of had stock gasket up top. im thinking maybe one of these is leaking? i dont hear an exhaust leak (had my exhaust studs and gasket replaced not long ago and havent heard any leaks since) but maybe one of the downpipe gaskets leaking could cause it to read lean at idle but not under wot?

[beacher1B0]

Idling and cruising at or around 14.7 is normal. That is what your ECU is shooting for with a properly functioning stock O2 sensor. You should actually be able to watch your AFRs while cruisin oscilate above and below 14.7 fairly rapidly. Say every other second or so. This will also let u know your O2 sensor for the ECU is operating properly.

IMO on full boost, safe zone is below 11.5.

[evolution23]

Idling and cruising at or around 14.7 is normal. That is what your ECU is shooting for with a properly functioning stock O2 sensor. You should actually be able to watch your AFRs while cruisin oscilate above and below 14.7 fairly rapidly. Say every other second or so. This will also let u know your O2 sensor for the ECU is operating properly.

IMO on full boost, safe zone is below 11.5.

yes i know 14.7 is stoich. for the engine. which is why i said im running at 16's at idle which is lean...

on a very hot sunny day (the days you get in your car and panic to roll down the windows) the car will fire up and idle at a perfect 14.6 - 14.8 and run perfectly. idles right, cruises right, boost right

i park in underground parking so every morning ill let the car warm up until i hear the idle change over and shes idling at 700, warms up rich (fires up at 12's, works its way up to 16) itll idle at 16's all the way to work (about a 15 - 20 min drive), while cruising it does change quickly (like usual) but is staying in the 15's instead of 14's. before while cruising i would see the odd jump to 15, but now im seeing the rare drop to 14. then when i get to work and its timing down its sitting in 15's and 16's

while boosting im still hitting high 10's, low 11's like before.

gauge has been in for a few months so i know how it was reading/acting before. im just a little concerned with the lean idle after i did water pump, idler, tensioner, tensioner spring, timing belt, cas gasket, valve cover gaskets, valve cover half moons, thermostat, coolant flush, removed bov recirc pipe. and just recently realized the shop did remove the down pipe when doing the clutch which has brought my attention to a possible exhaust leak now..

Hopefully that clears things up as i do know how the gauge should be functioning and is functioning properly. its just not reading the same at idle/cruise after parking for 2 weeks and doing some needed maintenance and sparked my interested and definitely threw up a caution flag in my eyes.

also been talking to some shops, some people tune their cars to idle at a 16 a/f ratio to keep the engine a tiny bit cooler at idle and to save a tiny bit of fuel i guess.. they said at idle and just cruising (no load) its not harming the engine unless it starts running 18+ so i am not nearly as concerned as i was when i first noticed it but its still on my mind everytime im driving the car which is everyday seeing as its a DD..

but all-in-all, im not very concerned about this anymore. was just looking for some input on the possibility of a possible exhaust leak causing it to read lean at idle.

[Skym]

His engine goes lean when cold (when o2 sensor is initially not looked at for A/F ratio adjustments), then doesn't if left for a period of time in the sun. That makes me think it's the ECU coolant temp sensor giving incorrect readings or something inside cooling system got stuck on coolant temp sensor.

Exhaust leak can allow oxygen to enter exhaust which o2 (oxygen) sensor can pickup.

Try asking someone to block end of exhaust for a short period of time (when engine is idling) while you listen for exhaust leaks around dumppipe (also known as outlet pipe or down pipe), etc.