Ongoing issue, possible vacuum leak or CCV?

[X5Kiwi]

For the last 2 months, my X5 has had the engine check light coming on for a few days, then clearing itself.

Twice it has been in to the dealer to get checked over, both times the check engine light has been caused by a fault on both oxygen sensors (before the cat) and both times they have been looking for vacuum leaks but have not found anything.

They don't believe that both O2 sensors have actually failed simultaneously.

After the second time in the shop, with the mechanic not able to find any faults, I drove approx 500 meters and suddenly got a constant miss fire. I returned to the dealer, and they replaced one of the coils, which fixed the miss fire. They suggested this might have been the cause of my previous problems.

However, only a few days later the check engine light came on again. The engine 'felt' fine most of the time, except under light load and below 2000rpm (i.e. driving up a slight slope in town) the engine would seem to cough a couple of times over about 3 seconds. Every day, on the same hill on my way to work. Also, my fuel consumption has gone up about 15%, without any driving style change. (The dealer did explain that with the computer registering faulty oxygen sensors, it would push the fuel map to full rich on idle, so this might explain this).

Today, however, the miss fire is back, continuously, even at idle. The check engine light is flashing. I called BMW, they suspect "a pipe that runs under the manifold" and have told me to bring it in on Monday so they can remove the manifold and check the "pipe" out.

I'm assuming they mean the crank case vent? From realoem it looks like there is a hose running under the manifold to the oil separator?

So my questions:
1. Does this list of faults sound like some sort of fault with the CCV or oil separator? I do NOT have any smoke coming out of the exhaust.
2. Any other ideas what could be causing these problems? I've already spent over $1000 on diagnosis, with no results.

[TerminatorX5]

you may have more than one coil misfiring and when they replaced only one coil the other ones went undetected...

do you know your exact codes logged in the computer? i've had similar issue with a coil, that logged all kinds of faults but one of the faults was consistent, that was coil #5 and variations of that cylinder... i also put the INPA (software that can program and monitor live motor data) into cylinder roughness test and let the engine idle - while engine idled OK, i noticed some changes in the sound of the engine, that never bothered me before - until i was able to correlate those "rumble-rumble-rumble-rrrumble-rumble-rumble" to the live view of cylinder #5... that extra "rrrrumble" was matching "nervous" movement of #5 graph bar... it made me think, that the coil #5 was not doing well, even without any load, and with the load it was just dying...


after i replaced the coil, the engine idled "rumble-rumble-rumble-rumble", without any extra "rrrr", and all the problems were resolved...

in your case, you may have more than one coil acting up and ALSO the spark plugs being fouled up...

I would not have taken the car to a dealer for the simple things such as coils, as they will diagnose the problem and throw parts at the car in hopes to fix the issue - AT YOUR EXPENSE...

you can get BOSCH coils on line (check ebay), and replace all of them yourself... spark plugs might be a bit more involved but still, doable...

try to get the actual read-out of your error codes, and if you are still taking the car to the dealer, see if they will let you see the live data - if they even check the live data...

[X5Kiwi]

BMW have replaced multiple coils for me over the last few years, so that I only have 3 of the originals now in the car.

When they suspected the coil was at fault a few weeks ago, they showed me the data on the computer, and they proved it was the coil by switching a good cylinder with the misfiring cylinder, and the misfire now started on the other cylinder.

As for replacing the coil myself, yes I could, but I have no way of diagnosing that the coil is faulty. What software etc can I use to check these error codes myself?

[epdarks]

Peake scan tool: Products

[tmv]

I bought a cheap OBDII code reader from Amazon for less than $20 to read SES. It's the Maxi-CAN 3000. For more involved diagnostic stuffs, I pull out my INPA/DIS laptop.
You can swap the coil like how the dealer did to test it.

[X5Kiwi]

This problem is still happening, and now I am getting a cloud of smoke for about 10 seconds when I start the car from cold.

Oil separator? CCV? BMW seem lost as to the cause, they just keep resetting the fault memory and sending me on my way.