AFC idle issue

[Wingman21]

^^^ You have a wideband? I know some narrowbands are pretty stupid and will say "lean" at idle even though the car is operating within normal parameters. Also, are you throwing a system too lean code? I would assume that running as lean as you say you are you would have a CEL. Because you say you run lean with the AFC both plugged in and unplugged I'd check for an exhaust leak around and before you wideband/O2 sensor. Last summer my wideband just started reading lean all the time and did everything I could think of - replaced both O2 sensors, the MAF and cleaned everything and it was still lean. It wasn't until a week later that I got under the car and really looked around (it had been raining all week) and I noticed that I was mising a stud on the s-pipe/j-pipe connection. I replaced that and everything was normal again.

I do not have a wideband, just a narrowband. I did throw a CEL (P0171) and the car is even stalling sometime so I guess my N/B does indicate the right thing (red light).

I will check for exhaust leak the next time I go under my car, but the only possible way would be around or before the first O2 sensor because the secondary sensor isnt involved in the mixture right? I did already check my manifold tough and everything is tied and no signs of leaks (black stuff).

 

[CustomMSP]

Guys,

A quick few words of advice...

Clamp all of your hoses that see any kind of pressure...including the PCV valve hoses down to the one connecting to the actual PCV valve. This will make a large difference in tuning and everything else. Also, I've just discovered today that the VICS and VTCS solenoids leak vacuum through the metal nipple that has the plastic cover on it. Make sure you plug it up for good. I stuck a tiny dowel inside the nipple and plugged it up with the same plastic cover. No more leaks there! Much better

 

[jamesk]

The thing I doesnt understand is that udner the over pressure settings, the signals should remain unchanged so even if the O2 isnt fully warmed up the ECU should be getting the same signals since the AFC is supposed to be transparent!

Also, plugging eh AFC without resetting the ECU again should still wortk beacuse the AFC is supposed to be transparent at idle! Am I right on this? I also find it weird that I am almost the only one with this AFC problem! Happened to me twice actually... two broken units !!!!!!!!!!!!!!!!!!

I know that I run lean sometime even with the AFC unplugged, but it is worst with it plugged. I checked for possible leaks and also switched MAF, so the O2 is my next guess, but then again sometime the car runs fine so thats weird! It is also only happening on idle!

no even though the values are at 10, nothing being touched the air fuel controller is still taking control. since the air fuel contoller is designed to clamp the maf sensor and o2 sensor, the ecu is fully relying on the air fuel controller to tell the car what to do. so the cells being at 10, the ecu is relying on the air fuel controller to tell the car to run normally.

so even though the values are at 10, the air fuel controller is still running the car and has control. if something is not right, then the car will react.

when they say at splitsecond that the afc turns on, they mean that the afc will start to be active, not necessairly turn on.

but the whole time, the afc is controlling the car. the ecu is fully relying on it.

 

[Wingman21]

no even though the values are at 10, nothing being touched the air fuel controller is still taking control. since the air fuel contoller is designed to clamp the maf sensor and o2 sensor, the ecu is fully relying on the air fuel controller to tell the car what to do. so the cells being at 10, the ecu is relying on the air fuel controller to tell the car to run normally.

so even though the values are at 10, the air fuel controller is still running the car and has control. if something is not right, then the car will react.

when they say at splitsecond that the afc turns on, they mean that the afc will start to be active, not necessairly turn on.

but the whole time, the afc is controlling the car. the ecu is fully relying on it.

Thanks for the reply once again. I appreciate your inputs. Although, I dont see how the AFC could have control on the ECU when it is not active. Under the overpressure settings, the signals of the MAF and O2 are simply re-writed on the output so the same signals reach the ECU like if there was no AFC in front. The only difference there could be is that the writing of the values isnt exactly the same so you get a weaker or stronger signal by just by a tiny bit, which might be enough to make the car run leaner or richer at idle since it is a very precise process! From my understanding, you could put any values that you want in the MAP under the vaccum columns and it should not affect the mixture since it is under the over pressure settings! Am I right on this?

Also, correct me if I am wrong, but the AFC purpose is to fool the ECU by making it think that there is less AIR coming through so that it pulls some fuel to make the car run less rich in boost. That part is for sure during boost (passed the overpressure setting), but for vaccum and idle, the AFC should not have any effect except maybe for that difference on input/ouput, which might be my problem.

Has someone already read an output signal from the AFC and compared it from its input when the unit is not active (idle or something) !? It should be the exact same signal! let me know if one of you has already done it!

Thanks

 

[terbow]

I do not have a wideband, just a narrowband. I did throw a CEL (P0171) and the car is even stalling sometime so I guess my N/B does indicate the right thing (red light).

I will check for exhaust leak the next time I go under my car, but the only possible way would be around or before the first O2 sensor because the secondary sensor isnt involved in the mixture right? I did already check my manifold tough and everything is tied and no signs of leaks (black stuff).

a leak in the exhaust will cause a lean at idle too. by exhaust i mean from the mani to the end of the cat. im not sure why but it does. when i had a diff exhaust on i didnt have a gasket inbetween the s and j pipe, it didnt have carbon but i could hear a small leak (car was slightly louder up front than normal), and i was running 17:1 at idle. once i fixed the leaks it went back down.

when my pritmary 02 went out, the CEL would be for system bank1 one too lean/rich. and it would go on and off sporatically. the 02 doesnt have to be way off to be broken, it just has to break certain perameters.

if i were u, i would fix it with the afc off, since u know its still happening with it off even if its not as bad. cause like jamesk said, the afc is always inbetween the signals (active or not, its hardwired and could be amplifying the problem if the unit is bad)

 

[Wingman21]

a leak in the exhaust will cause a lean at idle too. by exhaust i mean from the mani to the end of the cat. im not sure why but it does. when i had a diff exhaust on i didnt have a gasket inbetween the s and j pipe, it didnt have carbon but i could hear a small leak (car was slightly louder up front than normal), and i was running 17:1 at idle. once i fixed the leaks it went back down.

when my pritmary 02 went out, the CEL would be for system bank1 one too lean/rich. and it would go on and off sporatically. the 02 doesnt have to be way off to be broken, it just has to break certain perameters.

if i were u, i would fix it with the afc off, since u know its still happening with it off even if its not as bad. cause like jamesk said, the afc is always inbetween the signals (active or not, its hardwired and could be amplifying the problem if the unit is bad)

Ill check for an exhaust leak up to the cat then. Thanks for the input.

I got a call that my new O2 sensor was arrived so gonna pick it up tonight and try to install it sometime this week. I did throw the same CEL as you (bank 1 too lean P0171) so that might be my O2 that is going bad and like you said it can only be off by a bit, but its enough for the ECU to lean out the mixture since it thinks that its running richer for exemple.

I will definetly fix the problem with the AFC unplugged for sure, like you said, it might just be amplifying the problem. Just like I wrote in my previous post, the AFC might not be writing the exact values on the output channel so it might be a tiny bit higher or lower so the fact that my O2 signal might already be off, if on top of that the AFC change it a bit might be enough for the car to act crazier with it plugged. With a normal signal (functional O2 sensor), that tiny change might not be enough for the ECU to go crazy.

I just hope its the O2 sensor my problem... if not, well Im gonna have a new one at least hehe!

 

[solo.]

bump for updates because I'm having the same problem.

 

[Wingman21]

bump for updates because I'm having the same problem.

I havent had the time to change my O2 sensor, but should do it this week. Ill let you know how it goes!

Whats your problem exactly? Lean CEL as well?

 

[jamesk]

cleaned my o2 sensor with brake cleaner and the car runs much better. id advise you guys to do the same as well

 

[solo.]

I havent had the time to change my O2 sensor, but should do it this week. Ill let you know how it goes!

Whats your problem exactly? Lean CEL as well?

Well I have a wideband.

After resetting the ECU, my idle is lean (around 18-20) and it will stall out sometimes. After the CEL is triggered (P0171), the car idles back to around 14.3-15.7.

 

[Wingman21]

Well I have a wideband.

After resetting the ECU, my idle is lean (around 18-20) and it will stall out sometimes. After the CEL is triggered (P0171), the car idles back to around 14.3-15.7.

Maybe the car switches to an "open loop" mode when the cell is triggered to protect the engine !?

 

[Wingman21]

Update:

I just installed my new O2 sensor and the lean idle and sporadic stalls are still presents.

Any others thoughts?

 

[solo.]

Did you clean the EGR yet?
Also, what does the AFC say about vacuum?

I can blow through the WGA, so that might be a problem for me. As well, you can check if you have a vacuum leak too.

My car has been getting worse now, it stalls whenever I'm sitting 4 out of 10 times.

 

[Wingman21]

Mine depends. Sometime it can runs great and sometime it stalls after a while, when its warm. I havent check if it was still worst with the AFC plugegd in! I did check for a vacuum leak, but its hard to pin point and everything seems tight. I didnt clean my EGR valve either. I might do that this weekend, but just dont wanna break anything hehe!

 

[solo.]

Fixed my problem. It was my fuel injector insulators/gaskets. I had reverted back to stock injectors from the 440cc's and didn't change the gaskets, so there was leakage. I put the 440cc's back in and the idle is better now.

 

[Wingman21]

Fixed my problem. It was my fuel injector insulators/gaskets. I had reverted back to stock injectors from the 440cc's and didn't change the gaskets, so there was leakage. I put the 440cc's back in and the idle is better now.

So you were leaking fuel? Its nice that you find your problem hehe!

On my part, my car runs great sometime and some others, it wants to stall at idle. So its not all the time thats what make it weird!

DO you guys happen to know what is the difference between the IDLE when the car is still rolling and the idle when it is completely stop? It seems to me that the RPM for both are different, like 900 vs 750. When I have issue it is always at 750 so when I am completely stop!

 

[jamesk]

i do not see how the car would know the difference?

 

[solo.]

The car idles at 800rpm while in motion, when it's at a full stop, the rpms drops to 700rpm-750rpm.

My car had a vacuum leak because of the gaskets, not fuel leakage.

 

[Wingman21]

The car idles at 800rpm while in motion, when it's at a full stop, the rpms drops to 700rpm-750rpm.

My car had a vacuum leak because of the gaskets, not fuel leakage.

So you just tighted the screws or replaced the gasket?

 

[solo.]

I put the 440cc's back into the car as it makes the gasket sit tighter.

Just buy some throttle body cleaner and spray near your injectors, if the RPM changes, you need new insulators. If not, spray everywhere until you find the leak.