Tuning for Hanging Idle
Tuning for Hanging Idle My Silverado 5.3L T56 likes to hang the idle at 1500-1000RPM until coming to a stop where it will finally drop down to the commanded 650RPM. Some research suggests that the throttle cracker table needs to be reduced. However, what about reducing the "Desired Airflow" for idle? It has a mild cam (212/212 114LSA) and perhaps needs less air to idle? If I remove too much airflow, how can the PCM still reach the desired idle speed?
I guess the underlying question is, how does the PCM meet the desired idle speed if there is also a desired airflow? Seems like those two desires might be competing.
What is the downside to disabling the throttle follower? Looks like it's just meant to smooth transition from throttle to no throttle. It too adds airflow based on throttle and RPM.
I guess the underlying question is, how does the PCM meet the desired idle speed if there is also a desired airflow? Seems like those two desires might be competing.
What is the downside to disabling the throttle follower? Looks like it's just meant to smooth transition from throttle to no throttle. It too adds airflow based on throttle and RPM.
Throttle follower is different than throttle cracker.
Throttle cracker opens up the blade while you are driving to help with coasting, and to make sure the engine will not die while the vehicle is moving.
Throttle follower is independent function from anything. Its job is to just make sure that the engine rpm is controlled on a throttle blip. Smaller the number, the faster it comes back down to idle. Larger the number, the slower it comes back down to idle...
Larger throttlebodies usually need this adjusted to make it come back down to idle faster and to make the car sound more aggressive like a carb engine.
Throttle cracker opens up the blade while you are driving to help with coasting, and to make sure the engine will not die while the vehicle is moving.
Throttle follower is independent function from anything. Its job is to just make sure that the engine rpm is controlled on a throttle blip. Smaller the number, the faster it comes back down to idle. Larger the number, the slower it comes back down to idle...
Larger throttlebodies usually need this adjusted to make it come back down to idle faster and to make the car sound more aggressive like a carb engine.
Thanks for the help as always!
So should I even touch the "Desired Airflow" for idle? I believe this would also help the hanging idle issue. Perhaps there is too much base airflow for the cam.
So should I even touch the "Desired Airflow" for idle? I believe this would also help the hanging idle issue. Perhaps there is too much base airflow for the cam.
If it idles fine when you are not moving, then leave the desired airflow alone. Only fix and tweak the areas of the tune you are having issues with. In this case is moving airflow, which is the throttle cracker. It is setup by vehicle speed, so you can fix the areas that are a problem based on mph.
If it idles fine when you are not moving, then leave the desired airflow alone. Only fix and tweak the areas of the tune you are having issues with. In this case is moving airflow, which is the throttle cracker. It is setup by vehicle speed, so you can fix the areas that are a problem based on mph.
Much happier with it now. The RPM's also drop slightly faster between shifts which is nice. One thing I noticed is a slight gas smell from the exhaust when idling stationary now. Unless I'm mistaken, adjusting the cracker should not affect the stationary idling airflow
Next to try is the throttle follower. The Silverado tune has the follower airflow multiplier increasing with RPM, while the manual f-body is the opposite, perhaps to help high-RPM shifting?
I am having this same issue. Just did a tune on the dyno last night and made great numbers. The only hiccup is the hanging idle when going into neutral in an M6. RPM's stick to about 1300 and only come down with the clutch pushed in at low speeds. Looks like it may be the throttle cracker issue.
