BMW 330 Idle issues - CAT Automotive

We were asked to carry out diagnostics on a BMW 330i with a strange fault.

The vehicle came to us with a long history of repair attempts by a local garage, another diagnostic specialist and the main BMW dealer.

The repair history was vast including new spark plugs and ignition coils, new high pressure pump, new air mass meter and updates to the engine management system non of which had made any difference to the fault.

We were advised that when the car was hot if driven for 8-10 miles it would start to idle rough and run erratically. We tested the car and ran our normal diagnostic procedures the only significant fault was for lean mixture on all cylinders.

On road test the vehicle behaved perfectly until a distance had been covered and it would then produce the idle fault.

When the fault occurred it was running weak as indicated by both pre cat lambdas. We carried out a pressurised inlet smoke test but there were no leaks, all the live data looked normal and fuel pressure was good.

Previous specialists had concluded that this was an injector fault however this vehicle didn’t display any of the characteristic faults of poor injector spray patterns.

Poor injectors on this engine is quite a common issue but normally shows up misfiring and rough running from cold non of which this vehicle suffered with.

The fault would disappear after switching of the engine and would not re occur until a further road test was carried out.

After blanking off all external causes of a potential air leak the fault was still present. We concluded that the only other possibility was an internal air leak.

This particular engine uses a sealed breather system built into the rocker cover which comprises of a spring loaded diaphragm which is vented through the top of the cover.

After several attempts we eventually got the fault to occur for long enough to establish a large air leak through the breather to atmosphere. The cure was a complete new rocker cover as the breather is molded into the case.

BMW 330i with idle faults..

New rocker cover with built in breather..

Clive Atthowe Tuning Independant VW Audi specialists Norwcih

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Clive Atthowe Tuning

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Peng

02:27 10 Mar 25

My friend recommended me to go to this garage, but my car problem was not solved. Did the work but didn't find the focus.The following was updated on 11 FebruaryI can confirm that your garage has replaced the Haldex oil for my car and cleaned the Pump, but the reason I came to your garage is because of the error code of this Pump for Haldex Clutch, C1112 04 [008], not because my Haldex service has expired.At first this C11204 error code was read by OBD2 and they scanned the same error code after I visited the Volkswagen dealership in Norwich and asked to check the car (I had already fed this information back to you when I first visited the garage). I gave my car to your garage on the morning of December 14th. You scanned my car with VCDS and got exactly the same error code.Against this background, I have booked the Halxdex oil replacement in your garage on December 14th and checked whether the Haldex pump works. When the service was done Dale Lawson showed me my old Haldex oli. The oil was very clean and he showed a photo he had taken of the Haldex pump when it was removed. The photo showed that my pump had no glue on the strainer. When I asked my question "What was blocking the operation of the pump when the oil was clean and the strainer was not blocked", Dale Lawson replied "the pump was working, it was fine". Then I asked the second question, "What should I do if the error code comes up again?" Dale Lawson's lighthearted answer "Then change the Haldex pump"When I scanned the car again that night, I got the same error code. I was totally disappointed. After that I visited your garage and Dale Lawson was not surprised that my car had the same error code again and without further inspection he said he would replace the pump to solve the problem. The next step will be Haldex Controller ECU if you cannot solve it. And I distinctly remember him telling me that the Haldex pump on the car was fine and working.Finally, I would like to reiterate that my reason for visiting your garage is not to seek Haldex oil replacement service. It was because my car was throwing error codes and I wanted to talk directly to the garage to diagnose and resolve the error. To check whether the Haldex pump is working properly, the solution provided by the garage is to perform Haldex service. Visually inspect the pump and pump strainer while the Haldex oil is being replaced. If the pump strainer is clean and the oil is free of impurities, the ohm resistance between the terminals can be measured or a 12v power supply can be applied directly to the pump motor to test whether the pump is working properly. You and I both know that the point of doing this service with my car is to check that the Haldex pump is working properly, not to change the oil.You did not find out if the pump worked properly during the first Haldex service. We paid for labor and oil and wasted a whole morning. In the subsequent phone conversation, you said that you did not conduct a comprehensive check on the pump, but I clearly remember that your colleague told me that my pump was normal.This is only my true personal experience, and I admit that you are way ahead of your competitors in other areas. But you still lost me as an ordinary customer.

Glen whipp C.

11:23 28 Feb 25

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