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Hello.
I have a problem with my e46 320ci. The car wont idle and it feels like it doesnt have any power at all. It also runs very rough when i press the throttle and the rpms jumps up and down.
I diagnosed the car with an OBD scanner and it said it was a bad mass air flow sensor so i changed it with another one i had laying around that i know works. But the same happend. I started checking for vaccum leaks and i found out the whole intake boot was full of cracks. I replaced it with one i had laying around here but the same happend again. I took another diagnose and checked the voltage to the maf sensor and it said 0.03V when the engine isnt running and around 0,60-1 v when it is running, isnt this very low voltage? I searched on google and found out that the voltage should be 0.98v-1.02v when it isnt running and 1-5v when the engine is running. is this true?
I have searched all over internet and i cant find someone with this exact problem so if anyone knows the problem please help me!

Im very sorry for my bad english, im from Norway :)

Benjamin
 

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2000 E46 323i, 3.0L and 2.0L Z3's
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Welcome to the forum.

Have you cleaned your idle control valve? With the ignition on position 2 and the engine off, you should hear a humming sound under the inlet manifold. This is the idle control valve correctly doing its thing. If there is no sound, its stuck and definitely needs a clean. To clean it, you remove it and spray the inside with carb or brake cleaner. It should rattle easily when you shake it. Once its clean, spray the inside with a light oil say CRC5:56.

A couple of other test that may help you are below.

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 Z3’s or 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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Hello.
I have a problem with my e46 320ci. The car wont idle and it feels like it doesnt have any power at all. It also runs very rough when i press the throttle and the rpms jumps up and down.
I diagnosed the car with an OBD scanner and it said it was a bad mass air flow sensor so i changed it with another one i had laying around that i know works. But the same happend. I started checking for vaccum leaks and i found out the whole intake boot was full of cracks. I replaced it with one i had laying around here but the same happend again. I took another diagnose and checked the voltage to the maf sensor and it said 0.03V when the engine isnt running and around 0,60-1 v when it is running, isnt this very low voltage? I searched on google and found out that the voltage should be 0.98v-1.02v when it isnt running and 1-5v when the engine is running. is this true?
I have searched all over internet and i cant find someone with this exact problem so if anyone knows the problem please help me!

Im very sorry for my bad english, im from Norway :)

Benjamin
It is good to replace broken parts with new parts not old parts that have been lying around.

You have a scan tool.

What error codes does it show? What are the values of the short and long term fuel trims? These are sometimes called the adaptations on some scanners. Mixture and multiplicative. You should use this tool to diagnose the problem instead of guessing what comes next. Post your values.
 

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E30M3 Race F10 535 R1150Rt M Coupe
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Yes need to know about Multiplicative (long term) and Additive (short term) fuel trim data.

When we have that, we can rationalize if there is a vacuum leak causing the issue.
 
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