I just completed a pressurized smoke leak check on my intake manifold troubleshooting a high idle RPM problem.  Smoke check works very well!  No leaks except around the bearings that hold the throttle shaft in the Plenum.  Has anyone ever done a similar test?  Is it normal to have leakage around those bearings?

Really don't want to have to change them just to find out that wasn't the problem...

I've never done that test. I assume you've already verified FADEC throttle position sensors are 0% fully closed and the throttle idle speed screw is set 1-7/8 to 2 turns open. Maybe find a way to seal that up just for a ground run at idle... A nice blob of dough works surprisingly well with easy cleanup (flour + water, just don't twist the throttle). At least, it prevents you from replacing it and then finding out it didn't fix it.

Everything mechanically appears to be nominal. Borescoped the intake to confirm the butterfly valve is fully closed.  I tried Gorilla tape, will have to try the dough next.   Thanks!

Let me know how it goes!

Unable to find a way to adequately seal the bearings for a test because of the leak at the rear near the TPS's.  I cant get anything in this tight space.  Appears I may have to pull the plenum and replace the bearings.     I will report on the process.   First, just to eliminate the easiest first, I am testing the fuel injectors in case one is stuck open or something.

Yeah, it is a very tight space back there with everything installed and yes, I'd go right to the injectors after that. Let us know if either ends up working!

Quick update.  I pulled, cleaned, and tested all the fuel injectors and they all tested good.   So, I pulled the plenum.  It was pretty dirty, so I cleaned it.  I adjusted the throttle idle setting in accordance with the engine manual.  All working well.  I put a small bead of Blue Loctite around the bearing that holds the throttle shaft on the front, let it seep in and wiped away the excess.  I did not remove the throttle position sensors.

I re-installed the plenum using new high temp silicone tubes and smoke pressure checked for leaks.  Only leak is around the aft bearing between the plenum and the TPSs.

Test run went well.  I actually had to adjust the idle up.  I don't know which thing I did fixed it but it seems to be better now.  I test hover it today and hopefully all will continue to operate normally.  If it ever does it again, I will pull the bearings.

Hope your fix works.
   Can you educate me on what kind of fuel supply system you are using on your aircraft?

Interesting. I'm guessing it must have been your idle adjustment! Nice job, be sure to torque check all throttle related hardware between each next few test flights, it's not uncommon for a mishap to occur shortly after messing with that.

(01-24-2026, 12:42 AM)Sam Oliver Wrote: Hope your fix works.
   Can you educate me on what kind of fuel supply system you are using on your aircraft?

Standard Rotorway.  Two fuel pumps to 4 injectors.  The two secondary injectors although installed are not used with the Fueltec computer.  I run 100LL.