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General E46 Forum
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Old 06-27-2006, 04:07 PM   #1
RedBarron
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BAD MAF SENSOR Symptoms?

My car has had a very erratic and scwred up idle for quite some time now, the idle will drop down to around 300RPMS then back to a 1K rpms then settle and the car stalls every once in a while, So far I have replaced the ICV and that did not help at all, the idle is so bad I canít fix it Iím going to sell the car. When I disconnect the MAF sensor and drive it the problem is fix, the car runs perfect, well the idle issue is completely fix when itís disconnected but as soon as itís reconnected the idle problem reoccurs and it has slowly been getting worse. I have a ECIS intake so I think some old got on it and messed the sensor but, I wanted to get some input to make sure my assumption that the MAF is bad.
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Old 06-27-2006, 04:37 PM   #2
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Put your stock intake back on then see if will fix the problem.
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Old 06-27-2006, 10:12 PM   #3
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It could be your MAF, but I would try to swap in a "known good part" before buying a new one. The reason is that when you disconnect the a major part like the MAF, the DME sees that it is not there and can put the engine into a failsafe mode where it may ignore some other sensor readings or change certain outputs.

As an example, I was diagnosing a car that was setting misfire faults under specific rpm and load conditions. I disconnected the MAF, drove the car, and no more misfire faults. I swapped in a known good MAF and the faults came right back; I'm guessing that with the MAF disconnected, the DME simply stopped looking for misfires and just focused on making the engine run as well as possible without an important sensor.

Do you have any friends with a MAF you can borrow?

If the MAF doesn't fix it, and there aren't any faults stored for cam sensors or apparent voltage supply issues, I would take a look at the VANOS adjustment unit, especially if you have high miles and/or the symptoms happen mostly when the engine is cold. Good luck!
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Old 06-27-2006, 10:39 PM   #4
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the thing about a bad MAF is that it will usually give you a CEL. You might want to check your engine for vacuum leaks around the intake area - a lot of people seem to have a cracked rubber boot that connects to the intake manifold. I checked mine on my 01 and it has the beginnings of cracking.
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Old 06-27-2006, 11:24 PM   #5
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how much is a maf sensor
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Old 06-28-2006, 02:26 AM   #6
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Old 10-29-2012, 06:17 PM   #7
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I want to add that when the MAF is disconnected, the computer uses fail-safe parameters for the air/fuel mixture. It's not the optimum ratio but it allows the vehicle to function. Furthermore, the Electronic Transmission Control light may turn on and set the car in "limp" mode operating predominantly in 3rd and 4th gear.
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Old 10-29-2012, 06:55 PM   #8
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Unplugging the MAF will typically cause the engine to run richer on a fixed fuel map, many times covering up vacuum leaks or lean conditions.

Suggest you check out the first 2 links below in my signature.
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Solve your misfires, lean codes, rough idle - http://forum.e46fanatics.com/showthread.php?t=897616

Fuel pump failures - http://forum.e46fanatics.com/showthread.php?t=929501

Temp Info - http://forum.e46fanatics.com/showthread.php?t=964491

Hidden OBC Menu - Check Voltage, Temps, Fuel Level - http://forum.e46fanatics.com/showthread.php?t=239619

E46/E39 GM5 Door Lock Info - www.bmwgm5.com

Lower hose fan switch O-ring - BMW #13621743299
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Old 11-03-2012, 12:45 PM   #9
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Hoping someone can help me out. I have an 02 325ci and it dies on me at when press the gas after a complete stop. I can refire the engine and drive away. I recently bought the vehicle and the previous owner just replaced the MAF. I can also sit with the car in park and rev the motor. The engine rpm drop about 400-500 rpm and then catches up. I unplug the MAF and the stumble goes away. Any suggestions?
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Old 11-03-2012, 01:50 PM   #10
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I realize you are new here, did you read what I posted just above your question??

I also responded in same to your other post.

You do not likely have a MAF problem.

You need to get your codes read and read the first 2 links below in my signature. They will keep you rather busy!
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Solve your misfires, lean codes, rough idle - http://forum.e46fanatics.com/showthread.php?t=897616

Fuel pump failures - http://forum.e46fanatics.com/showthread.php?t=929501

Temp Info - http://forum.e46fanatics.com/showthread.php?t=964491

Hidden OBC Menu - Check Voltage, Temps, Fuel Level - http://forum.e46fanatics.com/showthread.php?t=239619

E46/E39 GM5 Door Lock Info - www.bmwgm5.com

Lower hose fan switch O-ring - BMW #13621743299
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Old 11-10-2012, 03:49 PM   #11
jayriv72
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Found an excellent explanation for the layperson that might aid in one's attempt at "diagnosing" their intake issues.

http://www.ehow.com/info_12225663_id...el-system.html

Anyhow, as mentioned in previous posts, it's a great idea to have your codes interpreted. It also doesn't hurt to thoroughly clean your ICV.
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