I have a hum coming down the air ducting from the throttle body with the ignition on but engine off.
Here’s a video link.
http://vid1382.photobucket.com/albums/ah270/littlebadger1/MOV_00011_zpsa1o8th40.mp4
Can anyone shed any light on this?
I worked out it’s coming from the idle air control valve.
Has anyone experienced this before?
Could a mod move this thread to Engine & Transmission please?
That’s the IAC valve vibrating at the frequency of the PWM drive signal from the ECU. Normal behaviour and nothing to worry about.
You say that it’s normal and Google searches say the same thing but I think there’s more than a coincidence here that all of a sudden I start to get idle/rev problems and the IACV start to hum at the same time.
Yesterday I cleaned the IACV, PVC and MAF.
Today I’m going to reset the base idle.
I’ll report back.
If you have idle problems and the valve is humming more loudly then usual then I guess it’s fair to assume both symptoms are related. If the idle was too high (due to a minor leak, split hose or something of the kind) then the IAC valve might close right down to try to reduce idle speed. If the valve were right at one end of its travel then that might account for increased noise. Resetting the base idle sounds like a good next move, though I’d also inspect the air hoses for any cracks, tears or abrasion.
I see you have the IAC on the pre-charger throttle (mine is under the DTB) and I imagine that would tend to make yours more audible.
Took it for a spin with the roof down.
Well the idle, hunting, surging problem seems to have gone.
I didn’t even reset the base idle.
In fact it’s now running better than before the trouble started.
I must make a note to make cleaning of the sensors a routine thing.
The IACV is still humming though.
Maybe it just doesn’t know the words 
I read that one on a page last night from a google search on my problem.
It appealed to my strange sense of humour (well I am Irish) and I could’t resist it, but my apologies, I know that it didn’t help you with your problem.
No need to apologise.
I’m sure it made some people chuckle.
Just an update on my car.
I did some motorway driving today and all I can say is that my car is just flying.
It seems the carbon deposits have been causing performance issues with my car as now just the slightest touch of the throttle and it just takes off like the Starship Enterprise going into warp.
May I recommend you look at cleaning your sensors and throttle body if you haven’t done it for some time.
Good to hear that the car is still running well. Nearly 15 years since I bought it new and 10 years supercharged.
I do look after it Nigel.
Now that I’ve fixed the problem I’ve fallen in love with her again and I’m looking at some suspension mods.
I can’t see me selling her as she’s that good.