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Old 02-15-2008, 04:58 PM   #1 (permalink)
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Default Car runs lean at idle 4-5 seconds after starting

I just noticed that my car is running around 15-15.5 AFR at idle and constant throttle. The weird thing is that when I first start it up it runs perfect for 4-5 seconds then my AF's go insane and start bouncing from really rich to lean and the finally settle at the 15-15.5 area. Also sometimes it will get worse and hit 16 at idle every now and then.

Ive checked for exhaust leaks, also have no boost leaks, my mods are
AEM wideband
Apexi SAFC Neo (which I turned off and it still did the same thing)
Needswings DP
PTP Wastegate
Big FMIC
Cold/Hotside hardpipes
Greddy Type-S BOV

Does anyone know what could cause this? I don't think its my wideband because I can feel the far react to the big lean spikes. I'm thinking of replacing the upstream o2 but I wanted to get some input before that.

Thanks
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Old 02-19-2008, 04:52 PM   #2 (permalink)
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Bump?
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Old 02-20-2008, 12:52 AM   #3 (permalink)
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15-15.5 is fairly normal. I usually bounce between 14.7-15.3.

As far as start-up...well, you hve to give your O2 time to get the heating element started. Untill it is, your car runs on pre-programed fuel maps, so it is a bit trippy.
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Old 02-20-2008, 07:50 AM   #4 (permalink)
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i have pretty much the same problem, except mine shows a little leaner(16s-17:1). i am almost certain that it is an exhaust leak. i checked my upstream o2 sensor with a scan tool and it is switching normally. my ltft at idle is 3%, and stft bounce between -2.5% and 3%. so, judging by the fuel trims, the car is not actually running as lean as the wideband is showing. this brings me to the conclusion that it is either an exhaust leak between the o2 housing and the wideband bung or the wideband sensor is bad.

big lean spikes are usually an igniton miss. that could just be plugs/wires.
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Old 02-20-2008, 11:41 AM   #5 (permalink)
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mine started doing this also. Found out my DP flex section is leaking
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Old 02-20-2008, 09:10 PM   #6 (permalink)
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See that was my exact problem before, the downpipe flex section was broke so I was running around 16.xx A/F with the downpipe open and 17.5+ with it closed. I fixed that and everything was perfect for about 4 weeks until this started.

I'm pretty sure its not a exhaust leak now because of the frequent lean spikes that cause the car to hesitate that were not there before.

Another thing now is that when I change gears now, engage the clutch and start giving it gas again the car stumbles/bucks very badly and then my A/F's spike lean to 17.5+ for a couple of seconds. The plugs are fairly new and were gapped right but tomorrow I'm going to go out and check/change those.

The only other things I can think of is upstream o2 sensor, wires/coil (although I do have a heat shield), or the fuel pump/filter.
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Old 04-28-2008, 10:51 AM   #7 (permalink)
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I'm getting the same thing. AEM UEGO shows between 14.7 - 17.1. bouncing around. I'm also noticing "Popping" at idle like hiccups. My cousin said that this is because the car is running "lean" at idle and that I should richen by tuning something in the throttle body?? Can anyone comment? Why is my car popping/hiccuping at idle? It sounds like a miss fire. Plugs are fairly new, NGK 4306's. I pulled them and they are grey normal burn. Also, the wires are Magnecore and are roughly 1.5 yrs old if that.

Please help!!
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