Cleaned MAF, idle problem
 

Hi,
I just cleaned my Mass Air Flow sensor with MAF cleaner. Now the car sputters at idle as if it is not getting enough gass. The car drives fine, its just when you fully let off the gas, it has to catch its self. I tried cleaning the sensor again, but no luck. I also reset the ecu with my AP just after I cleaned the MAF. Does anyone have any idea's on what the problem may be? Should I drive it for a little while and see if the ECU can learn?

Thanks,
Dave

Check your IAC valve. Little solenoid doohicky on the throttle body.

If you reset the ECU (and especially if you have mods) the car may have to relearn the fuel trims.

How do you check the IAC valve, what do you look for? Just took a ride and got P0171 (system too lean). I checked all the hosed and made sure all the hose clamps are tight, so shouldn't be a vacuum leak. Before I cleaned the MAF, the car ran fine, although I did get the P0171 after I cleaned and reoiled my air filter. This is why I decided to clean the MAF. I don't know what to do? Could the MAF be messed up now?

The IAC wouldn't cause a lean condition, just a weird idle fluctuation. Sounds like you have a MAF issue after all.

Sounds like a leak in the intake after the MAF to me. Or you broke the MAF... but that's usually all or nothing... like you wouldn't even be starting the car.

I was suspicious of a leak, but cant seem to find any. I just took it for a short drive, idle is getting better, but still acting slightly funny. My vacuum pressure at idle is usually a little less than -.05Mpa. When I let off the gas, vacuum pressure would normally go to that position, but now it jumps up to -.03 and has to catch it's self before it goes back to normal. It acting like it's running lean. The weird thing is that it was idleing fine before I cleaned the MAF. There is a good write up on the code P0171:
http://forums.nasioc.com/forums/show...ighlight=PO171
I checked the small vacuum hose that runs off the engine block, that is secure with a hose clamp. Maybe my O2 sensor is dirty, should I try cleaning that?

Check and make sure the active base map is correct. If the map you've been running only existed as a real-time map, you'd revert to whatever basemap was on there. I'm just wondering if your running the stock map with mods or something.

Other than a bad/wrong map, it does sound like maybe a post-MAF, pre-turbo leak.

Yeah, sounds like air leak after MAF. Did the MAF o-ring tear? Is the afta-MAF hose on straight & tight? Did you happen to crack the turbo inlet hose while fooling around wiht stuff?

BTW is your intake stock?

I checked the MAF O-ring and found it to be frayed. Just bought a new o-ring and some silicone. I hope this works. I'll let you know

Thanks for the feed back.

Replacing the o-ring was not the problem, still idled like crap. So I put an extra hose clamp on the recirculating turbo inlet. I also decided to clean my O2 sensor. None of this fixed the problem. So I went to subaru and bought a new MAF sensor, praying that this would be the problem. He gave it to me at cost. This was not the problem either. Still idles like crap. I checked and double checked all the hose connections, but do not see any problems there. I'm stumped, it drives fine. Just the idle is having trouble. Where do I go from here?

Time to pressure test the intake.

Get a can of carburetor cleaner, and spray around the intake/hoses/lines/gaskets on the intake side of the engine, while the motor's running. If your idle smooths out, or jumps up in rpms, there's your leak.

I would like to pressure test the system, but don't know how to go about that. I just took off my IC to check everything. Nothing was loose, but I had to make sure. Put everything back together, started her up, idle was sputering. Drove around, got home, idle was normal with no check engine light. Is everyone elses vacuum pressure during idle at or a little less than -.05MPa? I'm gonna let the engine cool down, then start it back up. hopefully its good, this is frustrating :furious:

Just ran it again, threw code P0171 again. What would have changed by cleaning the MAF sensor, even replacing it??? Has rough idle as if its misfiring or bogging down. I tried spaying some MAF sensor cleaner on the connections, didn't change anything.

i bet i can solve it...

what mods exactly are you running

mods:
-stg2 AP protune (a while ago)
-cated dp
-perrin up
-greddy exhaust
-gruppe-s headers
-perrin IC+inlet hoses
-Short ram intake
-NGK iriduim plugs

think thats it,
I had my buddy, who is a mechanic, check the hoses. Everything looks normal.
Maybe I should get it smoke tested/pressure tested? Anyone know a good place?
Why would it idle fine before I clean the MAF, then idle crappy after cleaning?

you have a BOV ?

i have had your problem a few different times.

so i been down that road before.

As everyone has already said, you likely have un-metered air coming into the system after the MAF.

And while you think it is running fine on throttle, it is likely running lean which is not good. and the poor ecu is constantly trying to adjust fuel to compensate. I would stay out of open loop or you may hurt something.

Have you followed Cory's recommendation in how to find a leak? You likely loosened or cracked something or pulled a vacuum hose when cleaning the MAF.

But why were you cleaning the MAF? You must have had something wrong beforehand to cause you to do that.

Do you have all the mods when you were tuned? If not, that is likely the issue possibly combined with a leak of some form.

Try putting the stock intake back on.

I do not have a BOV. The reason why I wanted to clean my MAF was because every so often I would get the P0171 at low load. I read up and it said this could happen from haveing a Oil filter. I recently oiled my filter, then got the code P0171, so I decided to clean my MAF sensor. Now its not running well. I agree, there is most likely a leak, but I just can't find it. I had my car tuned with all the mods that are on it. I don't see how I could have cracked a tube by taking off the MAF. There are only two screws on it and a didn't pull or put any pressure on the tubing. I'm scared to drive my car now. Where is a good place to take my car to get tested?

if you want to you can come to my house and ill poke around for some of the things i have seen that happen commonly.

That would be very nice of you. I'll be at work until 6:30. When would be a good time for you?

w/e ill msg you my phone numba.

i have flood light so we can do it tonight, i can also pull my car out of the garage and pull yoursin W/e need to do

So I took my car into C and C today. They looked at everything, smoke tested with no leaks in the intake, fuel pressure is fine, MAF is fine, O2 is fine... Then they found a small crack in my header, which dayofpain suggested when he looked at my car, but we didn't see anything. This would make sense because the O2 senser was seeing less exhaust trying to lean the A/F mixture (i think). Soooo, i'm gonna put my stock header back on Wednesday and pray that this will work..

Thanks for the suggestions everyone and for looking at my car dayofpain. I will let you know if this works.

well im glad i helped. i really wish i could have taken a better look at your header. but the combination of my jack. the lack of stands and a really hot header inches from my face didnt make for the best i had.

wish i would have caught that when u were here.

I don't see how a header crack would affect your idle. The O2 sensor measures the A/F *ratio*, so even if there is a leak the ratio stays the same. But.. I hope it fixes your problem, and if it does I would like to know how.

At idle, you could easily draw atmosphere into the exhaust and then push it into the 02 sensor on the next pulse.

Negative pressure in the header/uppipe before the turbo? Even at idle - I dunno about that. Again - I hope it fixes it.

I'm putting my stock headers on tomorrow. I will probably let C and C weld the crack, then I might either heat wrap or spray paint them with black heat paint. I will post some pics and let you know if it works, praying that it works.

I'm stumped. I swapped my headers and put on new gaskets, but the idle problem is still there. Here is what C and C checked:
-smoke tested for vacuum leak
-fuel pressure regulator check
-MAP and MAF test
-O2 sensor check
-ECT and IAC tested
-Checked emmisions, ok when running, but very lean at idle, causing rough idle.

What next? fuel injector cleaner? try swapping to a stock air box?(don't know why this would be the problem, since I have been running 50k plus miles with the same intake). Get a retune? I tried switching maps, but no effect. Where do I go from here???

there is something that we didnt try here

.... if its the reason ill be really pissed off.

call me tonight and we can test for it.

the reason im not saying what it can be is because i would be embarressed we didnt try it first.

Did you put the stock Uppipe back as well?

Plug your AP cable into a laptop and dashboard/log with Enginuity.

You will probably find it hunting A/F, but maybe not.

Try the stock air box.

Flash it back to stock

Take it to Subaru

Tighten the gas cap? :lol:

I searched online for enginuity, but the website doesn't work. I no longer have a air box, but would be willing to try one if anyone has one laying around. The next thing is taking it to subaru. Phil recommended trying a differnt bov, since only idle running condition is lean.

Just for you...

ftp://benzfamily.gotdns.com/download

yeah we need a stock BPV. if anyone can let us use theres even for 10 minutes i really think this option has a shot at fixing it.

to PM either me or Ddubs and let us know if you can help us for a short time tonight or soon.

thanks

can't get the link to work.

Fixed the link above.

And you don't need a BOV, just pinch the vacuum hose and put a plastic bag over the return nipple and put the hose back on. That should eliminate it at idle.

You could probably just stick a couple fingers/thumbs in the holes/hoses for a minute too. (That's what she said)

I just checked all the vacuum hoses that enter the intake. When plugging them with my finger, none of them affect idle. The BOV vacuum hose does not effect idle either. I didnt try plugging the actual recirc hose that enters the intake from the BOV, but I don't know if that would effect idle. Could a faulty spark plug give a P0171 code? (I think it would throw a misfire code) It all started from the MAF sensor, but even a new one didn't fix that??

Dean, it won't allow me to download enginuity, I can get to the file though. Thanks for the link

Anyone have a stock air box laying around? I don't know what to do from here :?:

Fixed for real this time...

You can always dl Tari ECUExplorer as well.

This is a long shot...

Is this the first time you've cleaned the MAF since the tune? Maybe it was tuned with a dirty MAF and a clean/new one screws it up.

What size injectors?

the injectors are stock. My car got tuned about 3yrs ago. I tried switching between different maps to idle check with no luck. If the MAF was dirty this whole time, more air would be flowing by that the sensor wouldn't pick up. Wouldn't the O2 sensor have sensed a lean running condition?

I got enginuity to work. I was looking at the A/F ratio graph. Once you let off the gas and let it idle, A/F ratio jumps up(engine stumbles), takes a few seconds to recognize, then falls back down. What is normal idle A/F ratio? the reading was around 16=lean compared to stoichiometric 14.7.

I really want to try a stock air box. If someone is willing to swap with me just to check, i'll buy you beer :)

The idle AFR should be 14.7:1 +/-.3. If yours is idling at 16:1 then I would log your fuel trims at idle - short and longterm, and see what those are doing.

Just as a general note... normally when you let off the gas the AFR will spike up (lean out) as the engine falls in rpm with no load. But it should settle around 14.7:1.

I am 80% sure I have an extra airbox in storage. You can use it as long as you need it. I won't be able to make the meet tonight, but I live in NW Reno and would put in on my porch if I'm not there. PM me for my number.

if noone steps up to this, im bringing my wrenches to the meet tonight and stealing someones BPV, to see if it fixes it.

it meets all the of the criteria of his problems.

it just doesnt make sense why it would fail.

I have a stock STI BPV also that can be borrowed...

bingo.

As has been said, it should hover at 14.7 at idle. 16 is out of bounds. What were the learned and immediate A/F corrections running at.

Hunting only at idle can only be a few things.

Leak somewhere between the MAF and the O2 sensor.

Bad intake map.

Bad MAF or O2 sensor.

If the BOV is bad, pulling it and blocking all the holes should fix the issue at idle.

I have an after market BOV & plug you can try.