Silverhawk injection idle issue

[Greg Arehart]

I was flying TnG in the pattern this morning. After about the sixth pass, I found that it was difficult to get the RV9 to go down on final (WAY more so than a normal 9) and ended up going around on our 7500-foot runway. Second time around, same problem but I was anticipating it and made the landing fine. Turns out that the idle had suddenly changed up to ~1300 rpm - had to taxi to the hangar with a bit of brake to keep from going too fast.

Shut down, pulled the cowl expecting some sort of throttle cable issue. Found nothing obvious. Cable attached properly, moving the quadrant in and out, looks like the throttle lever on the injection body is moving to the stops, so it's not the cable. Idle adjustment stop screw seems to be in proper position, and in any case, it is unlikely that the screw has gone further in. I see no changes in the system that are obvious to me.

I've googled and found no obvious suggestions on what might be the problem. It is something that occurred suddenly, from one loop around the pattern to the next. I did not try a restart after shutting down to see if it was still idling high.

So, I'm looking for any suggestions on what might have caused this and potential troubleshooting methods as well as fixes (if there is anyone who has had a similar problem). Engine is a Superior IO-360, if that makes any difference.

Thanks,
Greg

[kkmarshall]

Possible intake gasket leak?

Keith

[DanH]

The idle speed can't increase that much without the introduction of more air.

From most to least likely:

Sniffle valve broken off.

Gasket failure.

Manifold pressure fitting broken.

Intake tube o-ring or sleeve failure.

Broken intake tube (gee, can that happen?)

[Greg Arehart]

Thanks guys, I'll be headed to the airport later today and check these things.

Greg