Rough idle

[jr325i02]

I have a 2002 325I. It was getting me Bank 1 Bank 2 too lean codes and MAF sensor low voltage. During that time the car would have a small RPM dip every time I drove it. So I bought a new MAF sensor, and now the car has a very rough idle. And I tried it with another brand new MAF sensor and it also gave me the same problem, very rough idle and it'll turn off on me. Where could my problem be??
Another note when I was driving my car up and down the street it would turn off. And now because of that the transmission light is on and everytime I shift the car jerks what's going on now with the transmission?

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[328 Power 04]

Vacuum leaks. Massive ones.

I bet the rubber intake boots are severely cracked.

Get a smoke test done and seal up all the leaks.

[bmwdirtracer]

Welcome to the forum.

First, allow me to say that since you probably used a generic OBD emissions code-reader to see the codes, there's a very good chance that they are wrong, and incomplete. BMW's really need to be diagnosed using a BMW specific diagnostic device.

However, we have to use what we've got, so let's assume the codes are correct. You won't be able to read the transmission codes with the generic reader, or clear them, either. But the transmission codes / light are most likely caused by the MAF issue....which brings us to the next question:

Where did you buy these new MAF sensors, and what name was on the box? If you bought it at a local parts store, that's a big mistake, and you should return it, and buy a good one, from a BMW specialist supplier. It should come in a factory box that says either BMW or VDO Siemens. For sensors, it is crucially important to buy ONLY OEM QUALITY PARTS.

However, "MAF low voltage" wouldn't have me throwing a MAF at the car right away. First, I'd check the wiring and plug; make sure the pins are clean, and not loose, and that there's no wire damage. Then , again, you need a decent scan tool, because you should watch live data for the MAF voltage with the engine running.

AND, you need a smoke test of the intake/ccv system, using a professional smoke machine for at least ten minutes. If you have a sizeable leak, that would explain your lean codes, your MAF code, AND the transmission problems. (The EGS, or transmission computer, is going to have fault codes indicating that the engine computer is giving it faulty torque-related data (because the engine computer doesn't know how much air is entering).

EDIT:
Here's a good MAF for your car:
https://www.fcpeuro.com/products/bmw...ns-13621432356

[bmwdirtracer]

I was too busy being wordy, and Abel beat me to the punch, with the most likely suspect, by far. But there were red flags all over, for the OBD reader, and the Autozoo MAF, so I felt the need to cover the bases.

I do agree fully with 328 Power 04 that the intake leaks are by far the most likely suspect.

[jr325i02]

Ok so I found out that my intake boot was ripped.. thank you guys a bunch!
As far as the MAF sensor I tried 2 different ones,
The AutoZone one was 140 "returned it" and I bought one from Amazon " not the best quality" but the car had a very rough idle with both to the point where it turned off.
But the original one worked ok the car never turned off with it " still needs replacing bc I get the low voltage code" and I already cleaned it with MAF sensor cleaner.
Another thing to note the car works better with out the MAF?

The problem with the transmission worked its self out. I took it for a drive and was running smoothly, think I got that code/ jerky transmission problem bc the car turned off on me while I was driving it, at very low speeds 3mph

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[jr325i02]

Yeah turns out that my boot was cracking...very big crack and I still need to inspect the rest of the system. Good thing is that my transmission is working normal. Gonna buy an new intake boot . Thank you guys
The strange thing is that the car works better with out a MAF sensor
Works ok with the original MAF and cuts out with the new MAF sensors, its the contrary to logical thinking

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[MIKYZZ4]

Because as was mentioned,replace BMW sensors ONLY with BMW OE or OEM Replacements.
Your vehicle doesn't appreciate those aftermarket sensors you purchased as replacements,
but works fine with the original MAF, as that is not the root cause of the problems.
The problem seems to be primarily the intake leaks, as they affect the MAF readings.

[bmwdirtracer]

The next boot in line will likely be torn also, on the accordion part which goes to the IAC valve. It's not easy to change, because the hose clamps are pointing the wrong way.

The MAF low voltage code is quite possibly really a "low flow" code, caused by the fact that your engine is sucking a ton of UNMETERED air that didn't go through the MAF.

I agree on the cheap MAFs. Return the crap Amazon one, and either buy a new VDO/Siemens one, or put the original one back on.

The car runs better with the MAF unplugged because it goes into open-loop, like an "emergency mode", because it has no reading for airflow at all. Be aware that this open-loop operation is overly rich, and isn't good for your engine.

[jr325i02]

Ok so I replaced the intake boot, cleaned the throttle body tried both of the MAF sensors and the Amazon one is crap... So I still have a rough idle gonna get a original one.
One thing is that my car turned off once when I was driving it I was going about 5milea a hr.. turned it back on and it had the transmission light on and it stated to jerk every time it shifted?

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[bmwdirtracer]

Take the car to a good BMW/Euro specialist shop, and have the intake / crankcase vent system smoke-tested for leaks. There are a dozen likely leak spots which you really can't see, which will cause EXACTLY the issue you have, and a smoke machine will find the issue within ten minutes.

Really, a good BMW tech could do a smoke test, a crankcase vacuum test, and scan the computers, all in less than an hour. One or more of those tests will almost certainly prove the EXACT culprit(s).

[MarcoZandrini]

Try www.bimrs.org to find an indie shop that specializes in bimmers in your area.

[jr325i02]

Take the car to a good BMW/Euro specialist shop, and have the intake / crankcase vent system smoke-tested for leaks. There are a dozen likely leak spots which you really can't see, which will cause EXACTLY the issue you have, and a smoke machine will find the issue within ten minutes.

Really, a good BMW tech could do a smoke test, a crankcase vacuum test, and scan the computers, all in less than an hour. One or more of those tests will almost certainly prove the EXACT culprit(s).

That's exactly what I am thinking, well I got the car smoke tested and it didn't have any leaks, tried another MAF sensor form a be and it was idling a little bit on the Rough Side. I asked about the cvc and he told me that he couldn't test for that bc it only works when it's on?
These are my codes..
202
203
228
227
146
I'm still thinking it might be my MAF sensor how many of these codes could be attributed to a bad MAF?

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[bmwdirtracer]

Good BMW diagnostic scan tools read in WORDS, not just numbers. I don't have a clue what those number mean, because I use excellent diagnostic computers which speak English. Please provide the words.

[328 Power 04]

202 Lambda regulating limit Bank1
203 Lambda regulating limit Bank2
228 lambda contol tolerance Bank 2
227 lambda contol tolerance Bank 1
146 VCC-Potentiometer 1 (?)

[bmwdirtracer]

Thanks Abel!

jr325, unlike me, Abel speaks numbers. And the first 4 codes say you've still got mixture issues, most likely intake leaks.

VCC? I don't know. That abbreviation isn't in my book.

[MIKYZZ4]

202-203 as described above + Post-Cat
146 Evap System Leak Detected(small leak) or Pedal Sensor Supply Voltage Pot 1 (MS43)

[jr325i02]

Ok so now I'm noticing that when I take my oil cap the car starts to shake? And it does have alittle vacuum on it

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