Idle Surging (Badd)
09-10-2012, 01:03 PM
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Idle Surging (Badd) I hope this is the right place to post this.
I believe I have a bad case of idle surging. Swapped my motor to an 02 ls1 with a cam, cam specs in sig. Before messing with the computer any, the car had a bad idle surge. My buddy has messed with the computer on his HP Tuners and set idle to 600(eventually going to raise it.) Not to sure what all he messed with but the idle got a little better and didn't surge for about an hour. Then it went back to surging going from 600 Rpm to about 1300 RPm then back down. And it just does this over and over, occasionally it will idle and not do it, but not for very long. Pulled out the IAC and didn't look like anything was wrong( but not to sure what to look for.) Anybody have any suggestions I will greatly appreciate it.
Thanks,
Mark
I believe I have a bad case of idle surging. Swapped my motor to an 02 ls1 with a cam, cam specs in sig. Before messing with the computer any, the car had a bad idle surge. My buddy has messed with the computer on his HP Tuners and set idle to 600(eventually going to raise it.) Not to sure what all he messed with but the idle got a little better and didn't surge for about an hour. Then it went back to surging going from 600 Rpm to about 1300 RPm then back down. And it just does this over and over, occasionally it will idle and not do it, but not for very long. Pulled out the IAC and didn't look like anything was wrong( but not to sure what to look for.) Anybody have any suggestions I will greatly appreciate it.
Thanks,
Mark
09-10-2012, 01:21 PM
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Open loop, the low RPM VE needs to be right for the
cam or it will be over-enriched, slow motor response to
air-step = surge. You need the 400RPM column to be right,
and you can't get any data there, so you have to do it by
gut, cut-and-try.
Closed loop, your headers are probably
messing up the O2 sensor response and mis-trimming
again to the rich side.
If it idles OK after (say) you idle it at 2000RPM with the
pedal for a minute, and then the surge comes on after
it's been sitting at 600 for a while, blame the O2s being
too cold.
cam or it will be over-enriched, slow motor response to
air-step = surge. You need the 400RPM column to be right,
and you can't get any data there, so you have to do it by
gut, cut-and-try.
Closed loop, your headers are probably
messing up the O2 sensor response and mis-trimming
again to the rich side.
If it idles OK after (say) you idle it at 2000RPM with the
pedal for a minute, and then the surge comes on after
it's been sitting at 600 for a while, blame the O2s being
too cold.
09-10-2012, 01:32 PM
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Open loop, the low RPM VE needs to be right for the
cam or it will be over-enriched, slow motor response to
air-step = surge. You need the 400RPM column to be right,
and you can't get any data there, so you have to do it by
gut, cut-and-try.
Closed loop, your headers are probably
messing up the O2 sensor response and mis-trimming
again to the rich side.
If it idles OK after (say) you idle it at 2000RPM with the
pedal for a minute, and then the surge comes on after
it's been sitting at 600 for a while, blame the O2s being
too cold.
cam or it will be over-enriched, slow motor response to
air-step = surge. You need the 400RPM column to be right,
and you can't get any data there, so you have to do it by
gut, cut-and-try.
Closed loop, your headers are probably
messing up the O2 sensor response and mis-trimming
again to the rich side.
If it idles OK after (say) you idle it at 2000RPM with the
pedal for a minute, and then the surge comes on after
it's been sitting at 600 for a while, blame the O2s being
too cold.
I really appreciate it.
09-24-2012, 03:02 PM
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I've heard this before. What's the fix for O2 sensors being cold, I assume replace them? Will the switching voltages be correct if the sensor is running cold?
09-24-2012, 06:02 PM
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09-24-2012, 06:34 PM
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Exactly - 900 RPM, good fueling, and a tweak to the IAC tables (base running, idle over/underspeed, etc.). The problem is the IAC is slow to react to the adjustment needed, so a larger movement is eventually commanded by the PCM. It's kinda like over-correcting a slide in a drift and constantly fishtailing. You soften the ability for the PCM to correct from the top down a little more than from the bottom up and it should be good to go. Learning needs to be adjusted too so that the idle trims don't fight themselves.
