descreening/idle?
TECH Senior Member
Joined: Nov 2001
Posts: 7,036
Likes: 1
From: Lake Zurich, IL
the misfires at idle scattered around you'll notice on a bone stock car, just so long as there's not 1 or 2 cylinders that are really high (much higher than others)
But yes, descreening the MAF can cause idle issues
But yes, descreening the MAF can cause idle issues
However the MAF is weighted low, in the airflow calc
at idle RPM so I would expect somethinjg else to have
more to do with it.
My car had idle shake and low levels of misfires from
new (stock MAF) - 1-4 per cylinder. I believe these
have to do with how the PCM deliberately swings the
mixture to get cross-counts (14.7 AFR is an average
and almost never perfectly true in the moment).
To prove this you would look at misfires in open loop
just prior to closed loop enable temps. There you have
a steady (though perhaps not exactly stioch, off by
whatever your fuel trims are, opposite sign) mixture
not being jerked around by the proportional fueling.
at idle RPM so I would expect somethinjg else to have
more to do with it.
My car had idle shake and low levels of misfires from
new (stock MAF) - 1-4 per cylinder. I believe these
have to do with how the PCM deliberately swings the
mixture to get cross-counts (14.7 AFR is an average
and almost never perfectly true in the moment).
To prove this you would look at misfires in open loop
just prior to closed loop enable temps. There you have
a steady (though perhaps not exactly stioch, off by
whatever your fuel trims are, opposite sign) mixture
not being jerked around by the proportional fueling.
Thread Starter
TECH Resident
Joined: Apr 2005
Posts: 814
Likes: 0
From: NJ
umm im kinda understanding but not completely sense idont tune, but the car does not misfire at all after 1000rpms if i hold the gas to about 1000rpms its crisp according to my auttap and feeling it in my butt. but normal 800rpm idle has the shakes and 1-4 misfires scattered thru all cylinders. id say probably 10-15 total a minute at worst, so this could just be normal runnin from what uare saying huh?. well i maybe try gettin a screened maf and tryin it to see if theres a diffrence but thanks in advance for more info lol
It's certainly a worthwhile experiment to try, logging
a screened and a descreened stocker on the same car,
same air, etc.; log your TPS, RPM, MAP and both MAF
frequency and MAF airflow and dynamic airflow. Then
we can make a straight-up comparison of MAF reading
and how it's affected by the screen. Get a steady idle,
and 1/4, 1/2, and full throttle accelerations through the
top of 2nd gear and that should tell you everything you
need to know. I'll help you with the Excel crunching if
you take the data.
But back to the original question, I think the simple
answer is, it's normal (or intrinsic), and don't sweat it.
a screened and a descreened stocker on the same car,
same air, etc.; log your TPS, RPM, MAP and both MAF
frequency and MAF airflow and dynamic airflow. Then
we can make a straight-up comparison of MAF reading
and how it's affected by the screen. Get a steady idle,
and 1/4, 1/2, and full throttle accelerations through the
top of 2nd gear and that should tell you everything you
need to know. I'll help you with the Excel crunching if
you take the data.
But back to the original question, I think the simple
answer is, it's normal (or intrinsic), and don't sweat it.
