[GTwice]

Hi all
After experiencing rough idle and getting a DISA code, I pulled the intake manifold today and found out that small DISA valve has some play, while the big one doesn't have a flap at all! Completely gone, only the axis remains.
I can't find the flap anywhere - nothing is rattling in the manifold, intake ports are clear. Any ideas where to look? Could it split in half?
Is it possible that it failed earlier and somebody already took it out, and I was driving all the time without this flap? Would the engine run normally without it?

[E92William]

The engine won't run as good as it could without it but it would drive fine as long as it's not stuck in some runner. From my experience pulling manifolds with sometimes broken flaps. The large flap likes to hide in these two large runners, it gets stuck there if it fell as a whole unit and you have to hit the manifold with your hand a few times to get it to come loose

Is your shaft worn off the top bearing surface? If it is then the flap could definitely just have come off of it, often it breaks the shaft off though that's a weird scenario you have here. Would be really odd if the previous owner just took the flap off and put this back in

[GTwice]

Thanks for the advice. I tried bumping, shaking, poking inside it with every flexible tool I have and I found zero evidence that the flap is anywhere in the manifold. The DISA shaft is worn enough that it can be pulled from the top bracket, but not enough to let the flap slide off without using excessive force. I think someone must have removed that flap previously.

Anyway, I've installed 2 new DISA valves, car runs OK, although still has some light RPM oscillation during idle, otherwise everything fine.

[E92William]

That is very weird that it doesn't even have the flap laying in there at all. Guess as these cars age people will do half ass stuff like this when things break.. Do you have any codes? What do the fuel trims look like?

[GTwice]

Yeah, it got worse again, rough idle, even occasionally stalling. Drives fine under power. After a few miles yesterday, it finally threw a MAF code (a few actually). I was looking for vacuum leaks but none found so far - I was afraid I broke something when removing and installing the IM, but actually I that's what caused me to do this job in the first place.
I guess I have to try a new MAF tomorrow, I read also that a MAF plug could be the culprit. INPA is showing me about 3g/s during idle, that's way too low I think?
Any other ideas? I'm moving on wednesday, have to drive a 1000 miles, so I'm kinda in a hurry.
BTW. I have a black top N52 - plastic valve cover with integrated PCV

[E92William]

I believe I have read around 4gs at idle or 4. something. You might want to try and look at your MAF closely or clean it. I haven't had issues with the connector except for one side of the clip tab that keeps it in place snapping but it still locks it in

[GTwice]

I've changed the topic title, then was about to post again with another round of guessing, but just before hitting "Reply" I went to check something again and found this bugger - yes, it's a hole in my Valve Cover. So it was indeed a vacuum leak.

I think it happened when I installed my engine cover for the first time in weeks. The hole in the engine cover is actually worn and the bolt went through, and it's just long enough that without those few mm of plastic it pushed on the surface below it.

So, new VC is coming in tomorrow and I should be back in business.

[JmitchR]

I'd just like to chime in here and say I recently had some pretty major issues with my large flap breaking up in my N52. This is a 3 stage conversion car with all brand new OEM parts. The flap itself was sucked in through the intake and the remains were eventually found laying on top of cylinder 6. Now I was assured by everyone I talked to there was no way this could happen, but low and behold after shoving a borescope in there and removing the head the debris was found and removed. Before that was done the large DISA was replaced, bosch coils were swapped for the delphi and new NGKs were put in. The car constantly "coughed" at idle and was down on power.

This thread is a bit old at this point, but if you're still having rough idle issues having the flap debris get sucked into the head is not out of the realm of possibility.

[bluewater328]

Originally Posted by JmitchR

I'd just like to chime in here and say I recently had some pretty major issues with my large flap breaking up in my N52. This is a 3 stage conversion car with all brand new OEM parts. The flap itself was sucked in through the intake and the remains were eventually found laying on top of cylinder 6. Now I was assured by everyone I talked to there was no way this could happen, but low and behold after shoving a borescope in there and removing the head the debris was found and removed. Before that was done the large DISA was replaced, bosch coils were swapped for the delphi and new NGKs were put in. The car constantly "coughed" at idle and was down on power.

This thread is a bit old at this point, but if you're still having rough idle issues having the flap debris get sucked into the head is not out of the realm of possibility.

Wow, I've heard of the pin breaking and getting sucked up, but never actually seen the flap broken small enough to get through the inlets. Usually it gets physically stuck outside. Strange it actually broke apart completely.