letting off gas, car seems to idle high
02-17-2008, 06:52 PM
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letting off gas, car seems to idle high When i'm cruising around and then let off the gas, the car usually goes into neutral...which is normal...but it seems to hold its idle fairly high and doesn't really drop until I come to a stop and then it takes a second or two before it goes to normal idle rpms.
Any reason why it does that? I don't recall it doing that w/the MAF tune but w/SD it seems to hold the idle fairly high and for too long when it's in neutral and i'm coming to a stop.
high as in maybe 1500rpm or so.
pLus when I go from park to drive the rpms jump up a little before they settle down.
Any reason why it does that? I don't recall it doing that w/the MAF tune but w/SD it seems to hold the idle fairly high and for too long when it's in neutral and i'm coming to a stop.
high as in maybe 1500rpm or so.
pLus when I go from park to drive the rpms jump up a little before they settle down.
Last edited by dubrado; 02-17-2008 at 07:11 PM.
02-17-2008, 07:38 PM
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It's semi-normal, PCM commands extra airflow when rolling
("throttle cracker"). If you happen to have additional non-
throttle-controlled airflow, or your engine torque model
(which pushes airflow demand) is messed up, like by about
any mod worth doing, the airflow needed from the cracker
function is going to be different and want massaged.
If the SD tune made the idle-range operation cleaner and
more efficient then that's one way the same airflow, would
result in a higher idle afterward. Though you would think that
closed loop it would all come out the same.
Just start shaving back on the cracker table until you start
to see idle stability problems coming to a stop (esp. start -
stop - start, like pulling out into the median; the jerkier the
pedal the more challenging it is for the PCM idle loop to stay
with it and not over / undershoot). I believe the cracker's
primary function is this - making a "soft landing" for the idle
loop, which is "mentally challenged" at on a good day.
("throttle cracker"). If you happen to have additional non-
throttle-controlled airflow, or your engine torque model
(which pushes airflow demand) is messed up, like by about
any mod worth doing, the airflow needed from the cracker
function is going to be different and want massaged.
If the SD tune made the idle-range operation cleaner and
more efficient then that's one way the same airflow, would
result in a higher idle afterward. Though you would think that
closed loop it would all come out the same.
Just start shaving back on the cracker table until you start
to see idle stability problems coming to a stop (esp. start -
stop - start, like pulling out into the median; the jerkier the
pedal the more challenging it is for the PCM idle loop to stay
with it and not over / undershoot). I believe the cracker's
primary function is this - making a "soft landing" for the idle
loop, which is "mentally challenged" at on a good day.
02-17-2008, 08:19 PM
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Just start shaving back on the cracker table until you start
to see idle stability problems coming to a stop (esp. start -
stop - start, like pulling out into the median; the jerkier the
pedal the more challenging it is for the PCM idle loop to stay
with it and not over / undershoot). I believe the cracker's
primary function is this - making a "soft landing" for the idle
loop, which is "mentally challenged" at on a good day.
