Forester idle problem

[MADMAL]

When idling the revs go up and down from under 1 to over 2. Any ideas on whats wrong?

[xxMELZxx]

You could have an air leak somewhere?

[Guest]

1 to over 2 what? 1000-2000rpm?

Could be your Idle Air Control Valve (IACV), when was the last time it was serviced and had some Upper Engine Cleaner put into it?

Chuck a can of U.E.C into the intake manifold (buy from your local subaru dealer approx $22, follow the instructions) and see if this improves the idle.

My foz was like this due to a dirty IACV and has a bit of a sticky TPS that causes a bit of idle fluctuation but thats because its been used SFA in the past 3 months.

[Guest]

air leak, airflow meter? when my leggy afm went it did the same sort of thing.

-smurff

[MADMAL]

Thanks for the info guys and gals 8)

[nztintin]

mine rev hunts from almost stall to just over 1k, has done from day one...

[WRXONP]

yes still havent fixed my idle problem..i cleaned the iacv a while ago and it didnt make a differernce...

on mine when i come to the lights and stop itl idle like i have cams ..it fluctuates between 800-1000 rpm (not like a TPS hunt though..) and after a while of it idling like that (sometimes 5 seconds sometimes 1 minute) itl just suss it self and idle fine at 800 odd... but then sometimes it will be idling fine then drop to near 500 and want to stall...

i am wondering if i just replace the iacv?? its like it sticks and it cant work properly but last time i had it off it didnt move sticky or anything like that...

stupid subys with their idling problems hahaha

[nztintin]

mines not a problem, never stalls so it doesn't bother me

[Guest]

 WRXONP said:

yes still havent fixed my idle problem..i cleaned the iacv a while ago and it didnt make a differernce...

on mine when i come to the lights and stop itl idle like i have cams ..it fluctuates between 800-1000 rpm (not like a TPS hunt though..) and after a while of it idling like that (sometimes 5 seconds sometimes 1 minute) itl just suss it self and idle fine at 800 odd... but then sometimes it will be idling fine then drop to near 500 and want to stall...

i am wondering if i just replace the iacv?? its like it sticks and it cant work properly but last time i had it off it didnt move sticky or anything like that...

stupid subys with their idling problems hahaha

mi idel is never right etha.havnt done anything with my tps yet.culd also be a faulty afm.

[Guest]

 nztintin said:

mine rev hunts from almost stall to just over 1k, has done from day one...

Classic signs of faulty AFM !

[WRXONP]

nah my afm is mint ive replaced it allready after the last one shat out...mine doesnt stall either it just wants to go that low haha...im pretty sure its the aicv or maybe tps cos if i crack the throttle the slightest to bring the revs up maybe 100rpm above idle if that its sweet as...either prooves that it could be the tps as its coming off the idle contacts...or it could be the aicv as it wont be getting used once the revs come up

[nztintin]

 Ichi Ban']

[quote name='nztintin said:

mine rev hunts from almost stall to just over 1k, has done from day one...

/quote]

Classic signs of faulty AFM !

really?

4 years driving and 6 track days havent made it go bang...... yet!

[Guest]

YEP - replaced 100's for this fault . I mean 100's

The fault only affects idle - not entire range ( Dealers call it the AFM hunt )

Look at the basic ECU inputs at idle

crank / cam

coolant

O2

TPS idle (switch or voltage) -depending on model

AFM

easiest test is to un plug AFM

and check

ISC is an OUTPUT - so unless there heaps of play in it - uncommon

then its a signal INPUT that is affecting the OUTPUT signal to be incorrect

Hunting up and down shows that the ISC is working

[nztintin]

so o2 sensor could cause it? mines poked (again)

[WRXONP]

i dont have an o2 so couldnt be that lol

could u explain how the MAF can be faulty on idle but not through the rev range??

cos the basics of the maf is that its a load sensor..so wouldnt it be f***ing out on load? i know when my last MAF went poos it would idle fine..rev up in neutral... soon as u put it on load it would miss and fart and bang and all sorts...new MAF fixd it straight away

[Guest]

im sure some one on here has mentiond before how to test a afm.but i cnt rember lol :

[WRXONP]

ohhh heres a point to all u guys...

and i would loooove ichi ban to explain this one ;D

When i run a few steelo wools and a silencer in my muffler to quieten it down....the idle is pure mint...never drops...never goes up and down...is allways constant ;D

but my old wrx ran fine with a straight through 3 inch

something to do with having no back pressure?

[Guest]

 nztintin']

so o2 sensor could cause it? mines poked (again)

DEF YES, O2 is an input that the ECU is looking for/at during idle and cruise

[quote name='sti8u said:

im sure some one on here has mentiond before how to test a afm.but i cnt rember lol :

MAF is NOT a load sensor - it cant tell 1000 rpm wide open - throtte to 6000 rpm overrun which have similar airflow

As to the exact reason behind idle issue and fine under full load - dont know

[WRXONP]

so can u explain the whole silencer / back pressure thing??

[Guest]

 WRXONP said:

ohhh heres a point to all u guys...

and i would loooove ichi ban to explain this one ;D

When i run a few steelo wools and a silencer in my muffler to quieten it down....the idle is pure mint...never drops...never goes up and down...is allways constant ;D

but my old wrx ran fine with a straight through 3 inch

something to do with having no back pressure?

Your changing the air flow thru the engine obviously - (steelos are best keep in the kitchen and handled by girls)

So you must be putting the AFM (or MAF) into a airflow zone where where its faulting

ISC will compenstae to cover this by either raising or lowering "steps" - (a scan tool would show this change clearly when theAFM is not faulty)

Fairly simple really - hope this is ansered to your satisfaction !

[WRXONP]

the airflow through the maf would be exactly the same at 800 rpm with or without back pressure though wouldnt it?

[Guest]

and could we please move back to the forester that is having idle issues?

the OP is probably lost now coz of WRXONP trying to show off and be the man BS.

MADMAL fozzy help only please.

-smurff

[Guest]

NO, a low back pressure will not require the same airflow to maitain the same RPM

Think of it as the engine being slightly loaded with more backpressure - so will need more air to do same rpm as "unloaded engine"

[Guest]

 smurff said:

and could we please move back to the forester that is having idle issues?

the OP is probably lost now coz of WRXONP trying to show off and be the man BS.

MADMAL fozzy help only please.

-smurff

Sorry ! slap on the hand for me too

[Guest]

WRXONP - WTF

Ummmmmm No thanks for my explanation?

Did I actually answer a question that you thought i couldn't?

or do you think i'm wrong ?

If so why?