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Discussion Starter · #1 ·
Hello e46 people, I have a 2001 325ci convertible with manual trans. I have it for almost 2 years and the most annoying problem it always had was the unstable idle RPM. Most times when I pull up to red light and let go of throttle the RPM start surging up and down, sometimes to a complete stall, giving it good rev puts it out of this surging harmonic but it happens again at the next red light. A/C compressor seems to amplify this issue.
It shows negative fuel trims when it does that, but yesterday on a highway CEL appeared with "Bank 1 too lean" and "MAF values too low".
Previously I discovered when I remove one of the rubber plugs at the back of the intake manifold therefore create a vacuum leak it helps reduce this issue 馃拋, but I had put it back after fixing the PCV few days ago and it got worse.

What I did so far in an attempt to fix it (I'll expand the list if I remember anything else):

1. Replaced cracked valve cover with m56 metal one, pcv is from m56 as well.

2. New ignition coils, new spark plugs.

3. Replaced DISA.

4. New VANOS seals.

5. New intake boot.

6. Cleaned/Replaced ICV from junkyard, seems to be in identical condition but just in case.

7. Removed post-cat o2 sensors.

8. New pre-cat o2 sensors.

9. Cleaned injectors/ Tested fuel pressure / New fuel pump / New Fuel filter.

10. Tested with junkyard MAF, no change.

11. Smoke tested intake, no visible leaks.

I use best fuel there is, the car is well maintained after every 3-5k km.

There are lots of threads with this issue and some have solved it but unfortunately it didn't work in my case.

Any idea where to look at for the solution?
 

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The first step in diagnosing a problem is to scan the engine computer (DME in BMWspeak) for codes. I bet P0171 and P0174 will pop up. They are vacuum leak codes. You鈥檒l need to get the intake manifold professionally smoke tested. Try www.bimrs.org to find a reputable indie shop that specializes in bimmers in your area.

Stop throwing parts at the problem. Doing so wastes money, doesn鈥檛 fix the problem and it angers the BMW goddesses.
 

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Discussion Starter · #3 ·
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I did professional smoke test many times and most of these parts I replaced were vacuum leaks...
Here's what my scanner shows when I got the CEL on a highway.
The first step in diagnosing a problem is to scan the engine computer (DME in BMWspeak) for codes. I bet P0171 and P0174 will pop up. They are vacuum leak codes. You鈥檒l need to get the intake manifold professionally smoke tested. Try www.bimrs.org to find a reputable indie shop that specializes in bimmers in your area.

Stop throwing parts at the problem. Doing so wastes money, doesn鈥檛 fix the problem and it angers the BMW goddesses.
 

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Discussion Starter · #10 ·
And here's the log right after I stopped playing with throttle pedal to unbalance the idle, I stopped playing with throttle pedal and started logging right after that, so those fluctuations you see in this log is the car trying to stabilize the idle and almost stalls at some point, then it stabilizes.
 

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

A curious case, this one.

Firstly, I know you are new with OBD Fusion. Could you please set the OBD Fusion refresh/snapshot time to "PID Frame". You have it set to 100ms. Your OBD Fusion setup has a round trip of about 5 seconds between snapshots. So, for the second log, I have around 250 lines of data that gives me 5 data points.

The First Log
  • Total fuel trims range in the 3% to 10% lean range. Bank 1 is worse than bank 2
  • Load and RPM are stable and at sensible numbers.
  • Pre-Cat O2 sensors are switching but showing a lean off-set. This lines up with the total fuel trim numbers.
  • Post-Cat O2 sensors are ranging in the 0.25V to 0.6V. Possible a blocked cat indication.
  • MAF is showing a slight Over reporting condition. Over reporting MAF's cause Rich conditions. Your problem is a lean condition, so the MAF is not the cause. No need to change the MAF based on these results.
Apart from a slightly lean condition, there is nothing wrong with the engine.

The second Log
  • The engine is nice and hot and running in closed loop control. There is a blip into Fuel Status 4, which is used for high acceleration or deceleration. It's curious that it is here on a stationary car.
  • Total fuel trims are extremely negative (rich). -20/25% (rich) and rise through to 10/15% (lean).
  • The new pre-cat O2 sensors are showing extreme lean conditions. They never get above 0.3V. They should be switching between 0.1V to 0.8V
  • In Post#1, you say that you have removed the post-cat O2 sensors. Yet there are signals in the logs. Have they been re-installed? They are giving signs of blocked cats, that is, generally sitting around 0.3V or less.
  • You are getting a Bank 1 Lean code P0171
  • You are getting a P0102 MAF low signal/circuit code
The reason why removing a vacuum cap improves the engine running is because it is so rich at idle. The extra un-metered air is off-setting some of the rich conditions and improves the running.

There are only so many items in the basic engine control circuit:
  • Fuel: Pressure and volume. Too much, not enough, none, poor control. You have cleaned the injectors, replaced the pump and filter. The assumption is that without a pressure test result, the fuel system is good.
  • Air: Volume. Too much, not enough, none, poor control. You don't have any significant vacuum leaks. Smoked tested and pulling the vacuum cap with engine results point to this. Silly question, have you ever looked at the air cleaner filter?
  • Pre-Cat O2 Sensors: Too much, not enough, none, poor control. These are new, there are not O2 sensor codes. They work correctly in the first log and give interesting results in the second log. Lets say that they are good and telling the truth.
  • MAF: Too much, not enough, none, poor control. You have tried a junk yard MAF and done the MAF unplugged test. The first log shows a slightly over reporting MAF. Assumption is that the MAF is good.
  • Poor Control: If the Fuel/Air primaries are good and the O2/MAF sensors are good, it just leaves control. It's almost as if the DME is loosing it's marbles at times and doing something strange. Remove the DME connectors and check each connector for oil/coolant ingress. Especially connector X60003. It's the really big one, number 3 when counting from the firewall to the bumper. Also remove the DME lid/cover and inspect the MOSFET's that drive the injectors and coils. These will the the rows of 6 little black cubes around the outside of the PC board. You are looking for signs of black marks or damage. Remember that the DME is an electronic board, so careful with touching. Don't go killing anything with static electricity.
  • Blocked Cats: The usual signs of blocked cats are poor performance. The fuel trims can be slightly rich or lean at idle, but quickly go rich (large double digits) as the RPM and load increase. They also impact on the MAF readings. The engine can't draw in enough air as the exhaust gases are blocking the way, so the MAF values are low. Yours are slightly high at idle. So while you have some signs of aged/slightly blocked cats, I do not think this is your main problem.

Check the Air Cleaner filter and the DME.

If you are still having problems, do the normal 3 logs as described in the OBD Fusion thread. OBD Fusion

Also do a Rev-Rise test as detailed below.

Rev Rise Test
Run your normal OBD Fusion log. Hot engine and Cat鈥檚, stationary car. The test is best done just after a drive. Slowly raise the rev's of the engine up from idle to around 3,000 rpm. I mean slowly. It should take you 3-4 minutes to do this test.

It takes some skill to do this test due to the lightly loaded engine. A little throttle change results in a large rev change. Don鈥檛 run up and down the rev range getting used to the control. If you stuff up the first part of the test getting used to controlling the small rev changes, then redo the test.

Time Invested: It's taken 2 hours this morning to work through your logs and write up this reply. Hope it is helpful.
 

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Discussion Starter · #16 ·
Wow, thank you, yes this is very helpful. You are right, I had catalytic converter removed long time ago (huge mistake), then I installed one from Mercedes when I couldn't bare with the exhaust smoke being sucked into the cabin somehow, so the post-cat o2 were disabled from the DME (at least I was told so), they told me they are sending the signal but the DME doesn't take it into account.
Regarding the air filter - I change it with every oil change, around every 4k km, it's fresh.
I had this revs issue even before removing oem cats and all this stuff.
 

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Discussion Starter · #17 ·
@NZ00Z3 Would a junkyard DME be plug&play?
I can just test it for few bucks without buying it.
The last guy who was trying to fix the DME map couldn't make the immobilizer work with the new map so he just bypassed it directly to the starter and installed a fuse just in case. You think that means I could just swap the ECU without any issues now and test it?
 

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2000 E46 323i, 3.0L and 2.0L Z3's
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Do the DME inspection before you head off to buy another DME.

There are 2 parts to the EWS security system:
  1. Crank enable/disable
  2. Drive away protection.
While the guy may have done a hard wire bypass for the crank enable/disable, the drive away protection needs a DME code change. Your existing DME may/may not have the code change. The junkyard DME will need to be set up the same as your existing DME. So, just buying a junk yard DME has a level of unknown success.
 

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Hello Driver-X,

You may have problems with vacuum leaks as these cars have a lot of problems with vacuum leaks but your description of the problem reminds me of one more thing. Around my part of the world unstable idle RPM floating up and down and especially when driving off and sometimes leading to stalling is a known issue caused by some Valeo alternators. It happens with Valeo alternators and doesn't happen with Bosch. Some people advice that you can disconnect the connector of the alternator (it will not charge even though the big + cable is still connected) then start the car and see if the idle rpm is stable. I haven't checked if this test is safe to do so you have to check if you'd like to try it.
 
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