Help - Lean Idle
Sep 6, 2009, 01:48 PM
#1
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Help - Lean Idle
I just got done installing my FMIC and now I have a lean idle. It idles around 16.0. While cruising, AFRs fluctuate between 14.5 and 15.2 (normal I think) and when I get on boost they drop to around 11.0 (again normal).
2006 Evo IX Tuned for Mods:
BR TBE
BR SS O2
Walbro Fuel Pump
BR MBC
BR Intake
BR UICP
Installed since tune:
BR Exhaust Manifold P&P - everything was fine after this install
BR Race FMIC
BR LICP
Other than the fact my A/F gauge reads lean at idle, everything else is fine. The car runs fine but that gauge reading scares me. I know it's not the O2 sensor because I just replaced it. I haven't really went WOT yet, the most I've done is 4th gear, 40% throttle, boost got to 13psi, AFR went to 11.0 while doing a quick little pull from 35-45MPH. Until I can figure out more about the lean idle, I'm afraid to beat it any more.
I've read it may be an exhaust leak. The DP to O2 leaks a little bit, but I think it has always been like this, even before the FMIC/LICP install, when my AFR at idle was around 14.7. I'm pretty sure this isn't the culprit.
I've also read it may be a boost leak. I did a boost leak test and the only place I hear air leaking a bit is the throttle body region. It's not a significant leak but I can hear it after pressuring the system for a few seconds. It's not an external leak (tried soapy water) so I assume the throttle plate is leaking a bit into the IM. When I move the throttle plate the sounds changes so I assume that is what it is. Again, I didn't touch this part prior to the FMIC/LICP install so I assume this isn't the cause either.
The only thing is that when installing the LICP, I let my wrench hit whatever thing is in that area and it made a spark. I have no idea what it is but it looks like a cylinder and has a lead attached to it with a rubber boot over it. Everything in the car seems to work fine after I did that, and I have hit this thing before and everything seemed to work after it. What is this thing that made the spark and could this be causing my lean idle?
Any suggestions as to what this might be are helpful. No CEL's so far.
Thanks,
Matt
2006 Evo IX Tuned for Mods:
BR TBE
BR SS O2
Walbro Fuel Pump
BR MBC
BR Intake
BR UICP
Installed since tune:
BR Exhaust Manifold P&P - everything was fine after this install
BR Race FMIC
BR LICP
Other than the fact my A/F gauge reads lean at idle, everything else is fine. The car runs fine but that gauge reading scares me. I know it's not the O2 sensor because I just replaced it. I haven't really went WOT yet, the most I've done is 4th gear, 40% throttle, boost got to 13psi, AFR went to 11.0 while doing a quick little pull from 35-45MPH. Until I can figure out more about the lean idle, I'm afraid to beat it any more.
I've read it may be an exhaust leak. The DP to O2 leaks a little bit, but I think it has always been like this, even before the FMIC/LICP install, when my AFR at idle was around 14.7. I'm pretty sure this isn't the culprit.
I've also read it may be a boost leak. I did a boost leak test and the only place I hear air leaking a bit is the throttle body region. It's not a significant leak but I can hear it after pressuring the system for a few seconds. It's not an external leak (tried soapy water) so I assume the throttle plate is leaking a bit into the IM. When I move the throttle plate the sounds changes so I assume that is what it is. Again, I didn't touch this part prior to the FMIC/LICP install so I assume this isn't the cause either.
The only thing is that when installing the LICP, I let my wrench hit whatever thing is in that area and it made a spark. I have no idea what it is but it looks like a cylinder and has a lead attached to it with a rubber boot over it. Everything in the car seems to work fine after I did that, and I have hit this thing before and everything seemed to work after it. What is this thing that made the spark and could this be causing my lean idle?
Any suggestions as to what this might be are helpful. No CEL's so far.
Thanks,
Matt
Sep 6, 2009, 02:41 PM
#2
lean idle will never hurt the car.... plus 15-17 seems fine to me. Also dont mistaken idle for WOT. The o2 sensor is in closed loop on idle and also the idle switch is engaged, therefore you will see a completely different a/f at idle vs wot. 11 flat AFR is very safe for a road tune. id tune for about 11.2-5~ depending on gas.
how are your fuel trims?
btw...... the thing you hit that sparked was the starter. Perfectly fine, do not worry about it. I've hit mine as well doing the pipes down there and it also sparked.
how are your fuel trims?
btw...... the thing you hit that sparked was the starter. Perfectly fine, do not worry about it. I've hit mine as well doing the pipes down there and it also sparked.
Last edited by tscompusa2; Sep 6, 2009 at 02:46 PM.
Sep 6, 2009, 03:58 PM
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Sounds like that exhaust leak may be your problem. During wot and crusing there is enough exhaust volume and velocity to get a more accurate reading. You may want to fix that exhaust leak and see if your wideband gauge reads better at idle.
If that doesn't fix anything it may be problem with the wideband sensor, but to confirm that you need to check your fuel trims. If your car cannot achieve a near 14.7 idle and it's maxed out adding fuel with fuel trims, it will throw a CEL for system to lean. Assuming your on a stock ECU...
If that doesn't fix anything it may be problem with the wideband sensor, but to confirm that you need to check your fuel trims. If your car cannot achieve a near 14.7 idle and it's maxed out adding fuel with fuel trims, it will throw a CEL for system to lean. Assuming your on a stock ECU...
Sep 6, 2009, 04:06 PM
#4
Sounds like that exhaust leak may be your problem. During wot and crusing there is enough exhaust volume and velocity to get a more accurate reading. You may want to fix that exhaust leak and see if your wideband gauge reads better at idle.
If that doesn't fix anything it may be problem with the wideband sensor, but to confirm that you need to check your fuel trims. If your car cannot achieve a near 14.7 idle and it's maxed out adding fuel with fuel trims, it will throw a CEL for system to lean. Assuming your on a stock ECU...
If that doesn't fix anything it may be problem with the wideband sensor, but to confirm that you need to check your fuel trims. If your car cannot achieve a near 14.7 idle and it's maxed out adding fuel with fuel trims, it will throw a CEL for system to lean. Assuming your on a stock ECU...
Sep 6, 2009, 04:44 PM
#6
+1
boost leak will give inaccurate vac reading at idle as well as lean it out.
If you don't have a leak tester either make one here: http://www.vfaq.com/mods/ICtester.html or buy it from machv here: http://www.machv.com/macvleaktes.html
boost leak will give inaccurate vac reading at idle as well as lean it out.
If you don't have a leak tester either make one here: http://www.vfaq.com/mods/ICtester.html or buy it from machv here: http://www.machv.com/macvleaktes.html
Sep 12, 2009, 04:13 PM
#7
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As noted in my original post, I already did a boost leak. I noticed a small noise, but I think it is the throttle plate leaking ever so slightly. I didn't touch this part at all yet, so it must have been doing it before the FMIC install as well which means this isn't the cause.
From what I've read and been told, the car should idle at 14.7 regardless. Mine has been around 16.0-16.5 once the car is warm.
Anybody have any other suggestions?
From what I've read and been told, the car should idle at 14.7 regardless. Mine has been around 16.0-16.5 once the car is warm.
Anybody have any other suggestions?
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Sep 12, 2009, 04:40 PM
#8
As noted in my original post, I already did a boost leak. I noticed a small noise, but I think it is the throttle plate leaking ever so slightly. I didn't touch this part at all yet, so it must have been doing it before the FMIC install as well which means this isn't the cause.
From what I've read and been told, the car should idle at 14.7 regardless. Mine has been around 16.0-16.5 once the car is warm.
Anybody have any other suggestions?
From what I've read and been told, the car should idle at 14.7 regardless. Mine has been around 16.0-16.5 once the car is warm.
Anybody have any other suggestions?
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