did You check your oil fill cap. if that seal it bad it can haunt You ,easy fit..............good luck.

The chase for the cause of the random misfires continues.
After being unable to find the cause I decided to take it into our local European Auto repair shop to have their high dollar diagnostic reader scan the X5.

He scanned the car, found the codes that I have already been dealing with.
Drove it and found nothing wrong. He "reset" the DME billed me $130. Before i got the car home I had several misfires and a glaring SES light. Reaffirming why I never take my vehicles anywhere for repairs.

Back at it again, I removed the DIAS valve again and inspected. I applied vacuum and rigged up a 12volt switch to ops check the valve. Really couldn't find anything wrong with it. I did replace the O-ring with a bigger one. When reinstalling the valve I noticed that the with the new O-ring the valve fit much tighter.

So as for now I have two trips into town (40 miles each trip) with no problems. Maybe I have it fix it with a new O-ring, or the SES light bulb has burnt out?

Ill keep you posted.

Ugh, thats a lot of work to find the misfire, hope that was it.

I like the possibility of the SES bulb burning out! lol
I bought the cable and software from the romanian guy on ebay, and havent been happier! its not terribly easy to use, but, its completely thourough! it has helped me sort out my X5 many times.

Oh, for what its worth, Upallnight, disconnecting the MAF/MAP sensor causes the computer to ignore the crazy readings it may be getting and goes into a limp mode. I had this issue once with a customers chevy, where the MAF/Map was bad and we couldnt get it to start! disconnected the MAF/MAP sensor and it ran long enough to get it to the shop and figure it out! disconnecting it will set a code, but at least you get home in limp mode!

Sartech good luck and its also very probable that youve solved your problem with the one O-ring. if you ever need a scan let me know, im just across the border from you and spend lots of time in bellingham / lynden !

Do a compression test. I have a 530I same engine and did the exact same as you, started repalcing the whole intake manifold/CCV/ignition/fuel system. Ended up with 175 psi on all cylinders except for #4 which was 100 psi. I was having a problem with #4 the entire time. I havent taken the car apart yet but with 135K I am having a hard time beliving it is rings. Im thinking a bent valve or a frozen lifter. Waiting for the weather to break and the X5 timing chains to be done before I tear into it. Always start with the most expencive problem and work backwards. LOL!

:iagree: The computer will see a cylinder with low compression as a weak cylinder and assume the cylinder has a misfire so it will shut down the injector and throw up a SES light.

Check out this video and see if this can help you. - https://www.youtube.com/watch?v=_Vo4fm0JDPY

I was just trying to suggest something similar.
It seems that the low tension piston rings in these engines will start getting carbon deposits, and hence low compression (anecdotal evidence points 99.99% to the cyl #5 P code). Check out this thread, it includes the above youtube vid, but has more info in it. Also, maybe try to use the "Restore" product: "Complete fuel System Restorer" - it's easier to use than the AC Delco product from the vid posted.

I went through a similar episode of encountering every engine error code possible. Turned out to be the engine harness connectors. During a high water situation after heavy rains, some of the connectors were contaminated with water & dirt. On inspection, the dealer found that none of the main harness connectors had any dielectric grease in them. The harness must have been installed "dry". A new harness eliminated all the issues and the good news was my auto insurance covered it under the comprehensive as "storm damage". Since yours is also a 2002, I tend to agree with those posts regarding the status of your electrical connectors.

2002 X5 3.0 273,500 miles
2004 325i 118,000 miles

SarTech:

Where did you ever end up with your misfire codes?

I am having a similar issue, although my misfire (P0300 through P0306) codes are not accompnied by any other codes, and only seem to occur when off the throttle at highway speeds or very little throttle at highway speeds. Occasionally they will get thrown at lower speeds.

I have replaced every sensor, smoke tested the engine intake and exhaust 3 times, did a compression test (all within 5%), and still have the issue. The truck runs great under load and at idle.

Pulling my hair out! I love this truck, but I think it soon needs to go...