Codes not adding up

abrad

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Feb 20, 2007
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210
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Location
New York
Make
Honda
Model
Accord
Year
2004
Miles
226,000
Engine
2.4
Previously had a post about throttle control issues, which turned out to be a bad throttle linkage - slot where the cable connected had broken, but I didn’t realize at the time there was a broke piece, as it looked to be open ended.

Now, I’m getting a P0171 code. I’ve sprayed carb/choke cleaner around looking for vac leaks, no change. I cleaned the maf sensor, but after a few days, the code comes back. So, I ordered a new Delphi maf sensor, and just installed it. Now, I immediately get codes P0102 & P0113 — maf airflow circuit low & intake air temperature sensor high. Thing is, I can clear the codes, and without starting the engine, the codes come right back on.

Car is running fine, but has a stumble under a hard acceleration between 30-45 mph. Normal acceleration no stumble. I’m thinking I got a bad sensor, but need to test a few things more. Primary test is the voltage - does anyone know which tab is the 5 volt?
 

grcauto

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Thing is, I can clear the codes, and without starting the engine, the codes come right back on.
That fail at key on tells us it's in the wiring or bad sensor.
When the PCM sees a failed MAF circuit it will figure load based on TPS, VSS, RPM etc. It will usually run OK like that.
 

abrad

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That fail at key on tells us it's in the wiring or bad sensor.
When the PCM sees a failed MAF circuit it will figure load based on TPS, VSS, RPM etc. It will usually run OK like that.
Yeah, I’m thinking bad sensor as well. For shits and giggles, I’m going to put the old sensor in, and see if it repeats. No repeat, then my thoughts are bad sensor…
 

abrad

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Yeah, I’m thinking bad sensor as well. For shits and giggles, I’m going to put the old sensor in, and see if it repeats. No repeat, then my thoughts are bad sensor…
Well, now I feel stupid. Went to swap out the new sensor with the old one, and apparently when I reconnected the harness, it didn’t latch completely. I never tugged it to ensure it was solidly connected.
Now it runs ok, but not at idle, keeps dying. Took it out for test drive, runs fine at speed, but wants to stall at stop sign.
 

abrad

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Does it do that with the sensor unplugged?
Didn’t seem to, just the instant on with the two codes. Now with the sensor connected, rough idle.

I had the battery disconnected overnight, so it “should” have unlearned the readings from the old sensor…
 

grcauto

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If it idles OK unplugged the sensor is bad. The MAF is a straight data. No learning.
 

abrad

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I unplugged it, idles fine. I’m now on my second MAF now. First one was Delphi, second is Cardone. Can’t believe both are defective for idle. Thing is, if I put the original in, it runs fine while connected, just that at some point it will throw a 171 code. Inspection is due in July, so I really need to get this issue cleared up…

I’ve read that Hondas can be real finicky if not oem, but these aren’t knockoffs I’ve bought…
 

billr

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Sounds more likely to be a wiring/connector problem than the MAF sensor. Have you checked the harness sockets to be sure they are all grabbing the sensor pins a bit (a "drag test" using a wire/pin same size as sensor pins)?

Have you checked the PCM connections? If the PCM can be opened easily for inspection, check soldering to the PCM pins that connect to the MAF. Well, check soldering all over the PCM; use a bright light and magnifier, no matter how perfect your vision is.

Is this the second MAF in the car, or the second recent replacement? Yes, it is possible to get two bad ones in a row; it has happened to me with an ICM. It is not a quality issue, I think, more the result of our present society's everything-is-returnable demand.
 

grcauto

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I unplugged it, idles fine. I’m now on my second MAF now. First one was Delphi, second is Cardone. Can’t believe both are defective for idle. Thing is, if I put the original in, it runs fine while connected, just that at some point it will throw a 171 code. Inspection is due in July, so I really need to get this issue cleared up…

I’ve read that Hondas can be real finicky if not oem, but these aren’t knockoffs I’ve bought…
Your old MAF is likely fine and the lean condition is being caused by something other than the MAF.
 

abrad

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Sounds more likely to be a wiring/connector problem than the MAF sensor. Have you checked the harness sockets to be sure they are all grabbing the sensor pins a bit (a "drag test" using a wire/pin same size as sensor pins)?

Have you checked the PCM connections? If the PCM can be opened easily for inspection, check soldering to the PCM pins that connect to the MAF. Well, check soldering all over the PCM; use a bright light and magnifier, no matter how perfect your vision is.

Is this the second MAF in the car, or the second recent replacement? Yes, it is possible to get two bad ones in a row; it has happened to me with an ICM. It is not a quality issue, I think, more the result of our present society's everything-is-returnable demand.
Second replacement. I got the car 2 years ago from my neighbor. It’s been running fine up till recently. Was having an idle revving issue, which turned out to be a broken clip on the throttle where the cable connects. Bought a new throttle assembly, which had a new IAC and throttle control already attached. That cleared things up immediately. Now, it started throwing the 171 code “occasionally”. I’ve not found any vacuum leaks (cause that was the first thing I checked when I had the previous idle revving issue), I replaced the intake tube going from the air cleaner to the throttle, as it was cracked.
Both new MAF’s have had the rough idle/stall issue, so I would be inclined to agree with the defective part thinking, especially that both are made in a country that mass produces everything with next to no quality control. As for the pin connections, each time when I put the original MAF back in, no idle problems, so on that note I will question faulty wiring.
This is getting to the point of major frustration!
 

abrad

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Your old MAF is likely fine and the lean condition is being caused by something other than the MAF.
I’m beginning to wonder that myself. The front O2 shows normal varying levels, while the rear is showing steady. Any idea what those levels “should” be? I will have to go back in and check to get the current readings, probably tomorrow as I have a going away party for our son who leaves next week for his first duty base in the Air Force.
 

billr

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So, you have three MAFs, the "old" one and two replacements? You say it idles OK with the old one; does it set codes with that? Do any of these MAFs set the same codes?

I suppose it is time to start making some voltage measurements at the MAF, but it the problem is intermittent it could be very hard to "catch in the act".
 

abrad

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So, you have three MAFs, the "old" one and two replacements? You say it idles OK with the old one; does it set codes with that? Do any of these MAFs set the same codes?

I suppose it is time to start making some voltage measurements at the MAF, but it the problem is intermittent it could be very hard to "catch in the act".
Yes, 3 MAF’s. The two new ones have low/rough idle, to the point of stalling. The car run fine at speed, just bad idle. If I unplug them, the idle is fine. The old sensor still works, but it throws the 171 code, Bank 1 too lean. Based on previous comments, I’m thinking the problem isn’t going to be the MAF, but something else.
Haven’t found any vacuum leaks, replaced the throttle assembly due to a broken cable holder on the plastic holder (can’t get just the plastic lever). That took care of the previous revving idle issue, then it started throwing the 171 code a few months later. If this had happened immediately after replacing the throttle body, I would suspect that. Now, after having beat my head on the throttle issue before solving that issue, now I’ve got this issue to wrack my brain all over again!
 

billr

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No codes with the new MAFs? I suggest you put the old on back on and verify that (only) the P0171 still sets consistently. If so, check some of the other basic stuff, like fuel pressure, compression, and injector flow/pattern.

Are you using live-data to compare MAF, MAT, and fuel trims with these three MAF sensors? There may be some good clues in that data. If you don't have a way to view live-data... get it!
 
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