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Diagnosing bad MAF (P0171)

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Old 07-16-14, 01:48 AM   #16
artbuc
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Originally Posted by vishesh View Post
Whoops, now that you mention it, I probably am thinking of the IAT sensor bulb (the amber colored bulb that is clearly visible in the MAF). But I also cleaned the two little wire elements that are hidden deep within the recesses of the MAF. So hopefully that's all there was.
Yes, if you cleaned the "hidden" wire elements you got it. It is quite easy to see the difference between dirty and clean wires.
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Old 07-17-14, 12:45 PM   #17
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Hi all, hoping someone can help by providing some measurements from a working RX300.

Background: I am getting a solid CEL with code P0171 (Bank 1 Too Lean). Having seen many posts identifying a bad MAF (mass airflow sensor) as a possible culprit for P0171, I'm trying to systematically test the MAF to diagnose whether it is bad. I'd prefer not to just replace the MAF unless I am pretty confident it is the culprit. (See my prior ClubLexus post here.)

I have a RX300 repair manual that describes some diagnostic steps for determining whether a MAF is bad. One of the steps it describes is testing the resistance of the MAF's IAT (Intake Air Temperature) sensor. Below are the relevant excerpts from the repair manual. I tested mine and am getting between 5,000-6,000 Ohms at ~ 76 degrees Fahrenheit, when it should really be closer to 2,000-3,000 Ohms.

Can anyone else check the resistance they are getting with a known good MAF and let me know? Should only take a couple minutes and all you need is a (Philips) screwdriver and a multi-meter.

Thanks!

P.S., I have already cleaned my MAF so that should not be a factor.
Can anybody help?
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Old 07-17-14, 05:12 PM   #18
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I measure 2.5kohm at 69 deg F.
Spec is 2.21k to 2.69k @ 68 deg F.
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Old 12-07-14, 04:47 PM   #19
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did you get resolution on this issue? Was it a bad MAF sensor?
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Old 12-07-14, 06:39 PM   #20
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did you get resolution on this issue? Was it a bad MAF sensor?
Yes, I think it was. I did some testing of the MAF using a voltmeter, per the instructions in the Lexus service manual (see my earlier posts in this thread). It was giving bad / out of band measurements, so I figured it must be bad. I bought a MAF pulled from a working RX300 and dropped it in. That was several months ago, and haven't had P171 come back. The weird thing was, the used MAF that I bought was giving roughly the same bad / out of band measurements on the voltmeter when I tested it. But it worked in making the CEL go away.
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Old 12-08-14, 06:47 AM   #21
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Great news. Also, if you dont mind, what year is yours? '99 or '00, I'd guess?
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Old 12-08-14, 07:45 AM   #22
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Great news. Also, if you dont mind, what year is yours? '99 or '00, I'd guess?
Yes it's a 1999
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Old 12-08-14, 04:07 PM   #23
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Yes it's a 1999
I figured, since no p0174 code. Mine is a 2002, and i had both 171 and 174, as well as 125. I replaced the (freshly cleaned) maf with a new one, and i appear to, hopefully, have solved the problem!
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Old 12-08-14, 04:07 PM
 
 
 
 
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bad, code, diagnosing, forum, iat, lexus, maf, maf sensor, p0171, resistance, sc, sensor

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