2001 BMW Z3

I started thinking more about a vacuum leak as a potential source of the noise. I had read about DISA valves on another forum, but I had dismissed this idea a few weeks earlier, as my shop manual seemed to indicate that only the four cylinder cars have DISA valves. Had I continued to read a few more pages, I would have learned that my car has an Intake Manifold Actuator, which BMW guys commonly/mistakenly refer to as the DISA valve. They are a common source of vacuum leaks and other nasty failures. They are also pretty easy to remove, so I figured that it would be worth looking at.

Here's the Intake Manifold Actuator in place, behind the upper intake elbow.

The actuator itself seemed to be in good condition, but the orange o-ring seemed to be crushed flat. I reinstalled it for the time being and ordered a new o-ring.

Around this time, I noticed a small crack on a branch of the lower intake elbow. It wasn't really visible from above.

So, I added another item to the parts order. It's hard to say for sure whether the cracked intake elbow was the sole source of the mystery noise, or if it was a combination of that and the leaky o-ring because I replaced them both at the same time, but (jumping ahead a little bit) the noise is gone. Together, the intake elbow and o-ring cost about $20.

My new intake elbow and o-ring had arrived. It wasn't until I tried to remove the old o-ring that I discovered that it wasn't an o-ring at all, but rather some kind of orange silicone. It took me about half an hour to scrape it all out in order to make room for the new o-ring.

As you can see, the new o-ring sticks out quite a bit. This made it difficult to get the new actuator back in place on the intake manifold. I pushed it in as far as it would go and then tried to pull it in the rest of the way with the two mounting bolts. Big mistake. I heard a snap and discovered that one of the plastic mounting tabs had snapped off, ruining the $200 actuator and bringing my progress to a halt for another day.

The new valve arrived with better looking orange silicone and I carefully installed the new valve along with the new intake elbow.

When I was fitting the upper intake elbow to the lower one, my hand slipped. I heard something snap and immediately saw coolant spraying straight up. I had cracked the small coolant return line that goes between the radiator and the expansion tank. $60 from the dealer...

At some point in the middle of all this, I also bought a new Crankcase Ventilation Kit from Bavarian Autosport. This is another maintenance item, as the oil separator commonly gets clogged and the vent hoses dry out and crack. This job wasn't really hard but it was time consuming and some of the connections were hard to get at. Fortunately, Bavarian Autosport has a good three part how-to video on Youtube.

Most of the old hoses cracked as I was trying to remove them. All this stuff gets snaked up under and through the intake manifold. You have to do most of it by feel.

The new parts are better insulated from the heat.

I was glad when this part of the job was over.

Now everything is back together and working as it should. I've had the car since October 16. Today is the first time that I've driven it to work.

I am happy.