Author Topic: High Pitched Sound Under/Around Throttle Body (Read 2798 times)

Nelson_40 · « **on:** July 17, 2011, 09:17:55 PM »

For starters have a listen http://www.youtube.com/watch?v=8KvbkLqqVRE

The sound I am concerned about is the squeal/shriek. This car is new to me, is throwing code 1215 which is responsible for the choppy idle in all likelihood, but the code is probably not related to the sound. I have ruled out all belts and pulleys through process of elimination. I have verified that the oil pump is working. Further I have removed and inspected the intake (upper & lower) twice for cracks without result, and sprayed every reachable mating surface with carb cleaner to check for leaks. So, that leaves me stumped. Is air backing up or leaking through one of the throttle body valves (maybe due to junky throttle cable? Is it a crack in the throttle body or in the intake that I missed? Is the idle control valve working strangely? Additionally the sound exists during both cold and hot engine temps, the sound comes in around 2000rpm during both acceleration and deceleration, and lasts until at least 5000rpm. Ideas, help?

DesktopDave · « **Reply #1 on:** July 17, 2011, 09:47:58 PM »

Did you pull the belts to troubleshoot them? That sounds like a bearing kind of sound...increasing pretty much directly with RPM. If it's not that, see if the noise comes from the front. The tensioner and timing chain have a long history of failures.

Code 1215 is an AFM failure...I'd say it's a different & unrelated problem.

Nelson_40 · « **Reply #2 on:** July 17, 2011, 10:06:18 PM »

Yes, I did pull all belts individually and then together to see if that fixed it, but no luck. To my mind the sound originally sounded like a bearing, thus I assumed it could've been the oil pump or the mains. But after more listening it sounds more and more like some sort of odd vacuum leak due to the shrill non-metallic sound. Two things lead me to say this, one the noise is not constant, two it sort of backs off during overrun/deceleration. The other interesting thing is that this noise developed only after I had the car back in running order and had driven it for maybe 20 miles.

Oh, yes, 1215 is for the afm, tried cleaning it, then swapping it and checking all of its exposed wiring, no resolution on that one yet, but that's another well covered issue on this forum.

DesktopDave · « **Reply #3 on:** July 17, 2011, 10:16:22 PM »

I thought it sounded a bit like resonance in the intake manifold. But that's usually a lower pitch thrumming. I have to admit I've never heard anything quite like that...unless you have a BOV somewhere on that thing...

Nelson_40 · « **Reply #4 on:** July 17, 2011, 10:55:47 PM »

Yes, it does sound uncannily like some cheapo BOV/electric supercharger/in exhaust turbo emulator things. After ruling out belts and pulleys I thought that it was maybe a throttle body gasket (which sounded similar but more quiet on my other car), but then I pulled the TB heater plate and reinstalled the TB with no change. I just cannot fathom how something that loud (and embarrassing) can have no noticeable impact on my butt dyno throughout every part of the rev band. Tomorrow I will change both lower and upper manifolds, but if that does not solve it I am going to be really confused.

DesktopDave · « **Reply #5 on:** July 18, 2011, 07:22:35 AM »

If you find out what this is...market it to the ricer punks! They'd love something cheap that sounds like a BOV.

Have you pulled the cam cover to check that yet? Maybe something will look pretty obvious. Post some pics (of that and your cam gears too) if you get a chance.

Nelson_40 · « **Reply #6 on:** July 18, 2011, 12:38:27 PM »

Solved it! Car is running great now, idling well and not throwing 1215 interestingly.

The issue turned out to be that the upper manifold had part of an old sleeve (the ones that are around some of the intake manifold studs presumable to align the manifold) left in it which didn't mate up with the full sleeve on the new lower manifold I installed. The total amount of sleeve that was left was under 2mm, so just enough to prevent a good manifold seal, create that sound, but not hurt engine performance, save the lumpy idle. Just goes to show on a car that's new to you inspect, inspect, inspect!

DesktopDave · « **Reply #7 on:** July 18, 2011, 05:46:25 PM »

Sweet! Good for you! I'll file that away for my upcoming book: "1001 reasons your BMW will throw a 1215 or 1221."