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Discussion Starter #1 (Edited)
I had a 171 code that was intermittent with no noticable drivability problems. After cleaning the MAF with some cleaner, we've been SES free for two-three months. Today, 172 shows up. So, I went from a lean to a rich condition.

Searching here, I found that people are switching O2 sensors (which one?) and MAF's. ie: same solution as for a 171.

Where should I start?

-Sphinx
2000 G20
 

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The rear o2 sensor apparently has no effect on the car, and is really only there to make sure that the CAT is working.
I changed out my front o2 sensor and my p0171 code is still there. You could try that as it's the cheaper route (usually), but I'm thinking that the MAF change will fix it.

*edit*
here is a link to one that is about 4x cheaper than the dealership (maf)
http://www.drivewire.com/infinitiparts/catalog/infinitig20airflowmassmeter.html
 

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One of the two O2 sensors is actually one of the input signals to adjust the air/fuel mixture by senting the emission status in exhaust manifold.
 

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Discussion Starter #5
Car was running fine. Then my wife called and said it stalled each time she'd try to drive it. And now she has a bit smell of gas coming from the exhaust (while the car is running).

when she cranks it up, the rpms drop a bit and then come back up to normal. And in braking it does the same thing. But now, it's getting to the point of stalling.

No codes or lights. (The 172 light mysteriously went away on its own).

Does that help us narrow down whether it's the o2 sensor or the MAF?
 

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It's your MAF! Swap it and the CEL will be gone forever!!! Well at least for a little while until the gremlims come back and turn it on for something else!

I was reading the FSM last night and I swear it said the rear O2 does infact have something to do with the air / fuel? I will have to go back and read it again tonight to make sure. I think only after the front fails then the ecu uses the rear. I hope this isn't true since I have two rear o2 sensor codes!
 

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Discussion Starter #8
Dumb luck is that drivewire is out of stock on them and I can't find the vendor on ebay that sold the OEM ones for ~$100.
 

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Discussion Starter #9
Update

Well, turned out that the ebay vendor just needed time to relist more MAF's.

Got one. I couldn't figure out why the MAF had 5 prongs, but the old one had 4. I plugged it in. Started it, ran like crap and in limp mode. Now, a P0100 and a P0172 code.

After almost giving up, I found out that I hadn't properly pushed the MAF plug all the way in. All done, runs ok, but I didn't have time to test drive it before coming to work. 172 went away, but 100 still remained. I didn't have time to clear out the 100.

Another problem that crept up in the last few days (b/f changing the MAF) is that the car is extremely hard to start and worse and worse each day. It might start, or it might not. Almost like it has a dieing battery. Tested w/ my multimeter. Got 13V across the battery and 14.56 with it running. So, that eliminates the battery and alternator.

So, I'm now trying to figure out if the starting issue is related to the MAF issue or whether I've got a starter going bad.
 

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is it left over from before or did this show up with the new MAF?
100 = MAF high voltage. circuit shorted/open or the MAF itself is bad
if it drives ok, reset it and see what happens
 

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Discussion Starter #11
No, the starting problem started 2-3 days before I swapped the MAF. If you mean the 100, that showed up after I swapped the MAF, but I think it was caused by the bad connection (human error). So, 100 should be gone tonight.

BTW, has anyone gone through the trouble of getting their ECU reflashed like the little paper that comes w/ the MAF says to do?
 

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No, the starting problem started 2-3 days before I swapped the MAF. If you mean the 100, that showed up after I swapped the MAF, but I think it was caused by the bad connection (human error). So, 100 should be gone tonight.

BTW, has anyone gone through the trouble of getting their ECU reflashed like the little paper that comes w/ the MAF says to do?
Nope, new maf worked like a charm w/o reflashing.
 

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Discussion Starter #13
Turns out it was the battery. Thank God for the 3 year free replacement from Costco!
With the new MAF, car is as good as new.
 
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