MAF sensor keeps screwing up (cleaning it fixes it for a day or two.)

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Hi all. Re. the Vibe/Matrix in my signature, 2AZ-FE 2.4L engine. I've posted about this before, but it still isn't resolved and I'm confident it's a MAF sensor issue now. I'm on my second MAF in about two years. The first one was a Denso first time fit and the second (current) one is OEM Toyota/Denso. I've had the same problem with both. I'll either get a MAF sensor range code, a p0420 code, a lean code, or combination of those fairly regularly. Whenever I check my long term fuel trim, it's always way off lean or rich (been consistently running rich/negative lately.) However, when I remove the MAF and spray it clean (which I've done at least 20-30 times for each) the LTFT returns to normal and the codes clear up. The problem is this only lasts a day or two on average. Once it was fine for about two months, but lately it's been a problem every other day. I've tried different air filter brands (Toyota, Denso FTF, Fram Ultra, Purolator One, Mahle currently) in an effort to diagnose this problem but they don't seem to make any difference. I did read that some MAF sensors are self-cleaning to an extent by getting hot, but I can't determine if that applies to mine or not. I really shouldn't have to include cleaning my MAF everyday as part of routine maintenance, but does anyone have any ideas as to why it works or what else I can check? I'm at a loss.
Much appreciated,
Jonas
 

Jonas

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Is it the O2 sensor?
Possibly, but I can confirm the MAF is malfunctioning per the service manual-namely the fact that it is out of range according to the test procedure. Engine warmed up, but not running, the MAF should read less than 0.45 gps and mine usually reads between 0.43 and 0.53 gps in that scenario.
 
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Jonas

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Or just wiggling the harness. The fact that the fault returns very quickly makes me think it's not dirt, but a bad connection or something.
That make a lot of sense. Maybe cleaning it/fixing it is a red herring and plugging it back in is what gets it to act right. Thanks.
 
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You are getting multiple erratic codes, clean battery terminals and make sure battery is good. The numbers for gps, engine warm, at idle are way off. Engine up to temp, low idle, no loads, the gps should be around 24.
 

Jonas

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You are getting multiple erratic codes, clean battery terminals and make sure battery is good. The numbers for gps, engine warm, at idle are way off. Engine up to temp, low idle, no loads, the gps should be around 24.
gps at idle/no load is usually between 2 and 2.7 gps. I was referring to the baseline reading with the engine off and I also fixed a misprint. I meant to put less than 0.45 gps, not 45 gps.
 

Jonas

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air leak?
Intermittent/variable exhaust leak? I am running rich lately, but the MAF readings are always out of spec when there is a problem. I did get a lean code a few months ago, but cleaning or just messing with the MAF fixed that too.
 
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You mention that you get several codes ranging from the MAF range, P0420, and codes for a lean mixture. All of the monitored parameters relate to a properly running engine so you should log some data and watch the numbers for a few miles to see what component is acting up. You need to monitor the upstream and downstream oxygen sensors along with the readings from the MAF. Pair this information with the long term and short term fuel trims to see the ratio signature. Pay particular attention to the downstream O2 sensor to watch for catalyst efficiency and hope that the catalytic converter hasn't become poisoned. Monitor the upstream sensor for slow response and ensure that it is awake and not sluggish to respond.

You have gone through the original MAF sensor along with two replacement sensors and still show a problem so I don't know how likely it is that you have 3 bad MAF sensors. Based on the age of the vehicle you may very well have a bad oxygen sensor or failing catalytic converter. You state that cleaning the MAF fixes it for a day but if it only fixes it for a day then it doesn't really fix it at all. I would look a bit more at the upstream oxygen sensor.
 
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Never had issues like yours… Just curious, do you use CRC MAF sensor cleaner. I do and works well. The above good post mentioned real time monitoring both O2 sensors and I suggest Bluedriver. The first O2 sensor works with the MAF to correct air/fuel, the second O2 checks the health of the cat compared to the first O2 sensor. Second sensor when getting real time data should be less jagged. If it is the MAF getting dirty there should be residue in the tube next to the MAF. There is two parts to the MAF and the very thin wire that needs to be cleaned usually is not visible. A port opening is where you squirt the cleaner. What is visible on the outside is a thermistor to measure intake temperature.

 
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Jonas

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You mention that you get several codes ranging from the MAF range, P0420, and codes for a lean mixture. All of the monitored parameters relate to a properly running engine so you should log some data and watch the numbers for a few miles to see what component is acting up. You need to monitor the upstream and downstream oxygen sensors along with the readings from the MAF. Pair this information with the long term and short term fuel trims to see the ratio signature. Pay particular attention to the downstream O2 sensor to watch for catalyst efficiency and hope that the catalytic converter hasn't become poisoned. Monitor the upstream sensor for slow response and ensure that it is awake and not sluggish to respond.

You have gone through the original MAF sensor along with two replacement sensors and still show a problem so I don't know how likely it is that you have 3 bad MAF sensors. Based on the age of the vehicle you may very well have a bad oxygen sensor or failing catalytic converter. You state that cleaning the MAF fixes it for a day but if it only fixes it for a day then it doesn't really fix it at all. I would look a bit more at the upstream oxygen sensor.
I will continue to monitor the O2 sensor readings and codes, but I should also mention that the upstream 02 sensor and catalytic converter were replaced about a year and a half ago when the engine was rebuilt.
 

Jonas

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Never had issues like yours… Just curious, do you use CRC MAF sensor cleaner. I do and works well. The above good post mentioned real time monitoring both O2 sensors and I suggest Bluedriver. The first O2 sensor works with the MAF to correct air/fuel, the second O2 checks the health of the cat compared to the first O2 sensor. Second sensor when getting real time data should be less jagged. If it is the MAF getting dirty there should be residue in the tube next to the MAF. There is two parts to the MAF and the very thin wire that needs to be cleaned usually is not visible. A port opening is where you squirt the cleaner. What is visible on the outside is a thermistor to measure intake temperature.


Good to know. Maybe I haven't been cleaning the hard-to-see wire thoughtfully enough. The resistor wire looks perfectly clean, but the one down in the tube is hard to tell. Also, the intake air temperature is usually warmer than the actual outside temperature by about 20 degrees. Is that normal since it's warmer in the engine bay?
 

Jonas

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Or just wiggling the harness. The fact that the fault returns very quickly makes me think it's not dirt, but a bad connection or something.
I think you nailed it. I checked my MAF output this morning, engine off. It read 0.54 gps (>0.45 = out of spec.) I simply pushed in on the connector harness and checked again. 0.43 gps - within spec. I cleaned the points of connection really well as I would have the sensor wires. Hopefuly this will give me a good bite and a reliable connection for more than a couple days.
 
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Or just wiggling the harness. The fact that the fault returns very quickly makes me think it's not dirt, but a bad connection or something.
What happens is the female "sockets" fail to keep constant contact with the male pins. First, I'd clean both sides of the connector. Then inspect both sides of the connector. Look for female sockets with an extra wide opening. You can CAREFULLY pinch the female socket "sides" together to make a proper connection.
 

Jonas

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What happens is the female "sockets" fail to keep constant contact with the male pins. First, I'd clean both sides of the connector. Then inspect both sides of the connector. Look for female sockets with an extra wide opening. You can CAREFULLY pinch the female socket "sides" together to make a proper connection.
Good stuff. Thanks.
 
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