Lean condition at low RPM + idle

[Wingman21]

Hi guys,

I am currently having lean mixture problem with my MSP and I am trying to pinpoint the exact reason. I did throw a CEL for P0171 and not my N/B is always in the lean section.


I already verified the MAF (switched it) so it is not that.
I checked for leaks as well, but could not find any. I tied up every possible clamps as well. My vacuum sits at 20 Hg so pretty normal I guess.
My exhaust manifold doesnt show any signs of leaking.My guess is a bad primary O2 sensor (already have one ordered so will see next week). In the meantime, I do have a sound coming from behind the engine. It sounds like and air whistling sound, but I am not sure with all the noise coming from the engine. Is it a normal sound that all of you guys have too? Would a leak be that loud even at idle? Also, if I would have a leak, wouldnt my vacuum be lower than 20 Hg !?

Another observation is that my AF N/B is showing a lean mixture, but the idle is still smooth sometime and I can here some very small pops in the exhaust! Arent those pops caused by a rich mixture (back fires) or it also possible with a lean mixture !?

Thanks

[Wingman21]

Nobody can help me?

[fellfrosch7]

When the car is at low/part throttle, the ECU is running in closed loop mode. The O2 readout is really only useful when the ECU is in open loop at full throttle. That's why you see most AFR gauges running pretty ricey patterns at idle, switching between lean and rich.

I would try cleaning out your MAF (even though you switched it) with some electronics cleaner you get at Autozone and see if that fixes it. If you're really concerned, you could get a wideband. Also, after you switched out the MAF, did you reset the ECU to clear the code, and it came back again?

[Wingman21]

When the car is at low/part throttle, the ECU is running in closed loop mode. The O2 readout is really only useful when the ECU is in open loop at full throttle. That's why you see most AFR gauges running pretty ricey patterns at idle, switching between lean and rich.

I would try cleaning out your MAF (even though you switched it) with some electronics cleaner you get at Autozone and see if that fixes it. If you're really concerned, you could get a wideband. Also, after you switched out the MAF, did you reset the ECU to clear the code, and it came back again?

Already tried to clean up the MAF yes! As for the O2, it is only used in "Closed loop" not opened loop. During opened loop the ECU doesnt take into account the reading from the O2 sensor, it just throws fuel blindly.

I didnt reset the ECU in between the switch; just the fact that my idle was still poor and lean confirmed that is was not my MAF that was the problem.

[505zoom]

Lots of things can cause lean idle. Exhaust leaks, intake plumbing leaks, bad o2, bad MAF, bad tune, overboosting... to name a few.

[Wingman21]

Lots of things can cause lean idle. Exhaust leaks, intake plumbing leaks, bad o2, bad MAF, bad tune, overboosting... to name a few.

I agree excpet for the overboosting... its very difficult to achieve that on idle lol!

The past 2 days have been great tough. I dont know if I fixed a leak without even knowing or something, but we'll see if it stays like that.

[fellfrosch7]

Well that's good. Maybe since you didn't reset the ECU when you switched MAFs, it was in fact bad, and now the car learned around it with the new one.

[Wingman21]

Well that's good. Maybe since you didn't reset the ECU when you switched MAFs, it was in fact bad, and now the car learned around it with the new one.

I switched it right back after I tried it so Im still using my original one!

[fellfrosch7]

Who cares, if it's fixed, it's fixed. :)

[Wingman21]

Who cares, if it's fixed, it's fixed. :)

Well so far, crossing fingers hehe :)!

My AFC is still not working properly at idle tough. I thought both problems were related, but it seems not. With the AFC plugged, the idle is leaner and sometime stalls. I checked every possible connections and re-uploaded the map/settings a few times, but no success!