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Discussion Starter · #1 ·
Hello,

I got the Engine Codes 1C and 1D: Mixture Control, idle, cyl#1-4 and 5-8 before.
After I replaced MAF sensor and all four O2 sensors (2 precat and 2 post cat sensors), fault code 1C was gone so far. But I still have fault code 1D Mixture Control, idle, cyl#5-8.
It looks like there is still some problem with cyl #5-8 specifically? I cannot figure out what that is. Do you have any idea? Please help. Thanks very much.

david
 

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Seek to understand,^Value
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Do you have any idea?
I have no idea to help you on the specific codes ... but perhaps the misfire diagnostic thread will help?

- How to diagnose a BMW E39 engine misfire (1) & a cold-engine intermittent misfire (1)
 

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Discussion Starter · #3 ·
Hi bluebee,
Thanks for your reply. I forgot to tell you that I also got random multiple misfires before. I changed all sparkplugs, but it did not help. Then after I changed MAF sensor, the misfire problem was gone. Only the fault code 1D Mixture Control, idle, cyl#5-8 is still there. My car is about 146K mile. Looks like there still some problem with mixture control on Bank2 specifically. I can only guess about fuel injectors on bank2. Is it possible that all 4 injectors on bank2 went bad?
Thanks,
david
 

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Freude am Fahren
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Could also be an O2 or air fuel leak.
 

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Discussion Starter · #6 ·
hey bro, did you ever figure out the solution?
Hi itscoo2pyopants,

Yes, I found the root cause of my problem is due to the cracking of the oil separator inside the lower timing case. This caused the oil leak from the crankcase to the air intake manifold. This oil then came into the combustion chamber. So it caused the mixture control will never be correct. Changing MAF, Oxygen sensors just can improve the mixture a little bit but cannot correct the mixture. I would suggest you to check the oil leak or air leak around the air intake manifold to trace the root problem.
Hope it helps.
--david le.
 

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thanks for your response, i have the same exact codes on my 2000 x5 with 50k miles. 1c and 1d.

i did have a couple hoses in the back of the engine (oil seperator hoses) that were falling apart. i replaced those as well as valve cover gaskets because they seemed to be leaking some oil too. it cleared my evap leak code but im still stuck on these ones. i wonder if the oil seperator unit is damaged?

changing the maf sensor cleared your 1c? i ordered a new maf sensor already, im holding off on getting the o2 sensors until i try to maf.

Thanks again for your help
 

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Discussion Starter · #8 ·
Check the hose going from the oil separator to the back of air intake manifold. If you see oil inside the hose, you have an oil leak. Then oil separator is likely the cause. Changing MAF is worth to try, but it won't solve the problem if you have the oil leak into air intake manifold.
 

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i took off the intake manifold cover (on the back of the engine) and noticed oil in the intake manifold. is that going to be the cause of the codes?

i will be replacing the oil separator, intake manifold cover, gasket, and misc hoses that are flimsy. sound like a good plan? is there anyway to clean the oil thats in the intake manifold? or will the code eventually go away on its own after replacing these parts?

thanks again for your help
 

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Discussion Starter · #11 ·
Oil inside the intake manifold is definitely one of the cause of these codes.
It sounds a good plan. You can use intake manifold cleaner for fuel injection engine to clean the oil inside. As long as the oil is still there, the mixture will never be correct, and the codes will still be detected.
Hope it helps.

--david le.
 

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so i replaced the oil separator, intake manifold cover, and misc hoses. drove for about 80 miles, thought i was in the clear. just got home and the check engine light turned back on... now its giving me the same 2 codes, as well as an OF-1A AND OF-1B code, mixture control OFF idle in all of the cylinders. my maf sensor came in the mail, i will try that. whats next? 02 sensors?
 

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You need to smoke check the intake. You will likely have a vacuum leak somewhere.
Youo should also perform a vacuum check of e crankcase to verify the crankcase breather system is operating correctly. I believe the spec for that engine is 22 millibar, but I'll need to double check that.
 

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You need to smoke check the intake.
I saw a thread on the carbon dioxide method (I think by cn90) ...

That's something I gotta do.

How do 'you' run the smoke test yourself?
 

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I saw a thread on the carbon dioxide method (I think by cn90) ...

That's something I gotta do.

How do 'you' run the smoke test yourself?
You need a smoke machine. Obviously, most people aren't going to have this equipment at home.
Perhaps you can rent one?
There is really no other way to positively, accurately, and quickly locate a vacuum leak.
 

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Discussion Starter · #17 ·
Hi itscoo2pyopants,

With an assumption that there is NO more oil leak into your intake manifold after the replacement of the parts you mentioned, now the possibility is the amount of AIR come into the combustion chamber was not controllable to reach a correct mixture with the fuel. As I understand, at idle speed, mixture control system is a close loop that involves the MAF, O2 sensors, Engine Control Module (ECM), and the secondary air system. So, I think the following reasons could be the cause of these codes:

-MAF malfunction --> gives wrong indication of input airflow.
-O2 sensors malfunction --> gives wrong indication of the oxygen level of the exhausted gas.
-the air LEAK along the path from after the MAF to the combustion chamber --> the ECM did not account for this amount of air leak and was not aware of it. This is an uncontrollable situation.

Is your car's idle speed is rough?

In my car, I replaced MAF and O2 sensor first. It did not help to resolve the problem. Then I replaced the oil separator and all of the gaskets in the intake system. The codes did not come back and the car is running very well.

Hope it helps.
--david le.
 

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^ thanks again for your help

Replaced the MAF sensor and cleared out the code. i drove it for 150 miles and no check engine light turned on. I took it to the emissions station this afternoon and PASSED emissions :) i think im in the clear :thumbup:
 

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I cracked my secondary air system hose that goes from the air pump to the secondary valve that sits on the air pipe between the two banks. I taped it for now but will order a new one soon. Would this cause this same code, vac leak?

I know the secondary valve closes after two minutes during first start so that would isolate this hose from the system. I alreadty replaced bothe the front and rear OSVs with new vent pipe.
 
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