Surging idle problem
Thread Starter
Teching In
Joined: Jul 2007
Posts: 35
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Surging idle problem I have been trying to figure this out off and on for over a year now. My dad has an 06 Silverado that he bought with some mods already in place. Here is what I know about it. It is a manual transmission truck with a 4.8. It has a Radix blower kit and, based on how it idles, I think it has some sort of aftermarket cam. The problem is every once in a while, it will stumble and surge at idle. It does it frequently when rolling up to a stop sign or traffic light. It is also really bad during low speed parking lot maneuvering. I have already bumped the idle up to almost 1200 RPM, and it still does it. Sometimes it stumbles so bad it will die. I'm using EFILive to tune it. It has an LC1 WBO2 sensor in it which I used to do an Auto VE tune and MAF sensor calibration. Nothing I have tried has fixed it. Other than this truck, I have no experience tuning gas engines. I feel I jumped right into the deep end of the pool and lost my arm floaties. I really need some help here. Thanks.
I had similar issues which were finally solved by adding airflow and the car wanted more timing at idle...
I would like to find some time to play with it more because it is running a lot of timing and seems abnormal, but it worked so far.
I would like to find some time to play with it more because it is running a lot of timing and seems abnormal, but it worked so far.
Aftermarket cams, especially big ones, blow air into the
exhaust and will fool the O2 sensor into believing the AFR
is lean in the hole. Then mixture pulls rich, the motor gets
slow to respond to step-air and the idle RPM loop becomes
unstable.
VE tuning by the wideband is subject to the same spoofing,
and you end up jacking your open loop fueling (VE, MAF)
chasing that ghost.
My recommendation is to use bidirectional controls to dial
the delivered AFR until you find minimum MAP for your
target idle RPM, with all the adaptive crap turned off.
This is going to be your real stoich. Note the indicated
AFR on the wideband and the narrowband average mV.
Do this for several points from as low as you can maintain
on RPM, to as high as wide open IAC can take you. That
will give you a pair of curves for target AFR and target
narrowband mV (you'll have to map that to airflow mode,
later).
Beware adaptive spark, which on some models / years
has crazy tables that "give up" at high error-RPM and
will make idle bistable. These tables should be monotonic
and not go back to zero at high error positions. Adaptive
spark also tries its best to "hide" the trouble the motor
has idling, and if you tune with it on you won't be
working the worst case.
exhaust and will fool the O2 sensor into believing the AFR
is lean in the hole. Then mixture pulls rich, the motor gets
slow to respond to step-air and the idle RPM loop becomes
unstable.
VE tuning by the wideband is subject to the same spoofing,
and you end up jacking your open loop fueling (VE, MAF)
chasing that ghost.
My recommendation is to use bidirectional controls to dial
the delivered AFR until you find minimum MAP for your
target idle RPM, with all the adaptive crap turned off.
This is going to be your real stoich. Note the indicated
AFR on the wideband and the narrowband average mV.
Do this for several points from as low as you can maintain
on RPM, to as high as wide open IAC can take you. That
will give you a pair of curves for target AFR and target
narrowband mV (you'll have to map that to airflow mode,
later).
Beware adaptive spark, which on some models / years
has crazy tables that "give up" at high error-RPM and
will make idle bistable. These tables should be monotonic
and not go back to zero at high error positions. Adaptive
spark also tries its best to "hide" the trouble the motor
has idling, and if you tune with it on you won't be
working the worst case.
Thread Starter
Teching In
Joined: Jul 2007
Posts: 35
Likes: 0
Thanks guys. This gives me some stuff to look at. I went by and picked up the truck this evening so I could try some stuff out, and it seems to be running pretty decent right now. I'll drive it around for a few days to see if it has any fits since the problem never seemed real consistent. I have to pull the tune out of the ECM because I really don't even know for sure what is in it. I've tried so many different things, I can't remember which one I used last.
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What Jimmy posted makes a lot of sense. My wideband reads lean at idle and I tried adding a lot to the VE table to correct it but never did get it right...I stopped once the car was running well.
My idle afr is 14.8-15.5, cam is a 230/238 with 8* overlap (IIRC)
I might go back and use Jimmy's method to see if I can clean it up some more and get the car to stop trying to idle with 28* timing.
My idle afr is 14.8-15.5, cam is a 230/238 with 8* overlap (IIRC)
I might go back and use Jimmy's method to see if I can clean it up some more and get the car to stop trying to idle with 28* timing.
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What Jimmy posted makes a lot of sense. My wideband reads lean at idle and I tried adding a lot to the VE table to correct it but never did get it right...I stopped once the car was running well.
My idle afr is 14.8-15.5, cam is a 230/238 with 8* overlap (IIRC)
I might go back and use Jimmy's method to see if I can clean it up some more and get the car to stop trying to idle with 28* timing.
My idle afr is 14.8-15.5, cam is a 230/238 with 8* overlap (IIRC)
I might go back and use Jimmy's method to see if I can clean it up some more and get the car to stop trying to idle with 28* timing.
Even when I had set it lower it was adding more timing itself up to about that point and my scans weren't helping me pin point it for some reason. After several weeks of off and on idle tuning, as soon as I got it to work right I kinda stopped messing with it.
Now that I'm not burned out on it I would like to try to go back and see if I can make it better.
Now that I'm not burned out on it I would like to try to go back and see if I can make it better.
