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Discussion Starter #1
First off I want to say that the car does not run rough as nails with the MAF plugged in however I notice an occasional and subtle shake at idle that is more noticeable on very cold starts, and the exhaust smells quite rich(I do have a decat, but even so the smell is quite strong) I have no codes and i can't see the rpm moving around i can just feel it. I have replaced :

Recently Cleaned ICV (And tried an icv delete tune, same shaking happens)
Engine mounts
CCV
Vacuum lines
Both intake boots
(and much more but these are the only things I can think that would affect this)

The other day I was refitting the intake system after doing the oil sump gasket and I noticed the next morning that the car ran smoother at idle, no more shakes, then I realised that I'd forgot to plug the MAF back in, plugged it back in and now the idle shakes are back. I do have a spare maf that I haven't tried just yet, my question is how dangerous will it be to run the car without the MAF temporarily, I have seen mixed reports as to wether the car will run more lean or rich without the MAF. And as an extra question which is recommended as a replacement maf, Delphi or Siemans VDO? I have heard Delphi is a decent brand however it is £67 and the VDO is £146 so the price difference concerns me a bit.

Thanks in advance!


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E30M3 Race F10 535 R1150Rt M Coupe
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Not dangerous, the DME is smart
However I'd scan it for codes ad to why it better disconnected.
 

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I ran mafless for 3 months when trying to figure out my limp mode issue. Turned out to be a clogged cat. With the maf unplugged, car wouldn't go into limp mode. It actually ran very well and I would get 27-28 mpg on a trip during that time.

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First off I want to say that the car does not run rough as nails with the MAF plugged in however I notice an occasional and subtle shake at idle that is more noticeable on very cold starts, and the exhaust smells quite rich(I do have a decat, but even so the smell is quite strong) I have no codes and i can't see the rpm moving around i can just feel it. I have replaced :

Recently Cleaned ICV (And tried an icv delete tune, same shaking happens)
Engine mounts
CCV
Vacuum lines
Both intake boots
(and much more but these are the only things I can think that would affect this)

The other day I was refitting the intake system after doing the oil sump gasket and I noticed the next morning that the car ran smoother at idle, no more shakes, then I realised that I'd forgot to plug the MAF back in, plugged it back in and now the idle shakes are back. I do have a spare maf that I haven't tried just yet, my question is how dangerous will it be to run the car without the MAF temporarily, I have seen mixed reports as to wether the car will run more lean or rich without the MAF. And as an extra question which is recommended as a replacement maf, Delphi or Siemans VDO? I have heard Delphi is a decent brand however it is £67 and the VDO is £146 so the price difference concerns me a bit.

Thanks in advance!


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Clean the MAF element wih MAF cleaner.
 

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Discussion Starter #5
I may just run without it until I have chance to get the spare maf in then, I have already tried cleaning the MAF and it made no difference. I also understand the Ecu isn't stupid but I know that disconnecting the MAF will make it 'dumber' just how dumb I'm not sure lol.

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I may just run without it until I have chance to get the spare maf in then, I have already tried cleaning the MAF and it made no difference. I also understand the Ecu isn't stupid but I know that disconnecting the MAF will make it 'dumber' just how dumb I'm not sure lol.

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It was one of the smarter dumb modes I've seen. You of course will throw a ses light and the sai won't actuate.

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Discussion Starter #7
It was one of the smarter dumb modes I've seen. You of course will throw a ses light and the sai won't actuate.

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My engine light didn't come on when I had the MAF unplugged not sure if it's because mine is a euro tune or because I only drove it 10 miles or so. Also if by sai you mean the air pump I've deleted that, my exhaust is catless anyway

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Discussion Starter #9
The DME reverts to a rich fuel/air mixture when the MAF is disconnected. Have you scanned the DME for codes?
Yes there is no codes whatsoever on the engine, I only have a code when the MAF was disconnected

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2000 E46 323i, 3.0L and 2.0L Z3's
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Some reading for you.

Do you have a vacuum Leak?

The proportion of unmetered air from a vacuum leak to metered air is higher at idle and lower at revs. Do this test.

With a hot engine at idle, check the 4 fuel trims, 2 short-term and 2 long-term. If any are > 8% then you likely have a vacuum leak. Rev the engine to 3,000 rpm for 30 seconds and watch the short-term fuel trims. If they reduce significantly, might even go negative, then it is confirmed that you have a vacuum leak. Smoke test the engine to find the leaks.

If the short-term fuel trims do not reduce significantly, then it’s something else.



Do you have a fuel supply problem?

The fuel supply system has to deliver 2 key functions:

1) Fuel pressure. It should be 50 PSI at the fuel rail Schrader test valve with the key at position 2 and the engine not running. The fuel pressure regulator is part of the fuel filter. It could also be the fuel pump.

2) Fuel volume. If your fuel trims are +/- 5% at idle, but get worse, > 8% when at highway speeds, then you could have a fuel volume problem caused by a blocked fuel filter or a failing fuel pump.



Do you have a faulty MAF?

The MAF should be drawing around 3.5 g/s at hot idle.

Make sure that the MAF is marked BMW or Siemens/VDO. The cheap Chinese knock-off MAF's or the Hyundai part number MAF's don't work well on the E46's.

Many people unplug the MAF and discover that the rough idle or lean condition disappears. They conclude that the MAF is faulty. This is not always the case. When you unplug the MAF the Engine computer (DME) reverts to using fuelling tables already programmed into it. These fuelling tables are richer. This richness often compensates for a lean running condition caused by vacuum leaks. So, confirm that you don't have any vacuum leaks before unplugging the MAF. If you then unplug the MAF and it does improve the lean condition, changing the MAF with a good quality one is your next step.
 
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