S40 V40: Maf curiosities Vs buzzing sound

[nokinnikon]

2003 S40. 1.8i B4184S2. 120,000 MLS, manual, petrol.

When i unplug the maf sensor she runs just fine, sat in carpark level ground I give it a burst of revs as it falls back to 750 Rpm idle I hear no bangs and pops in exhaust and she sounds wonderful, i then Go for a drive, sounds, feels smoother.

I then plug the maf back in and do exactly as described above and it's sounds like fireworks in the cat/centre/silencer. Go for a drive and it just seems, not right.

So question: is my maf sensor dead?

Secondly,

I've been chasing a buzzing sound when I put my foot down and under load (warmed up) it's coming from the front left, after checking all the heat shields plastic inners of wings, beauty panels, nothing, NADA. So i took to taking out the air cleaner box and checked all over for any possible cracks and looked inside at the cold air intake module and moved the two flaps inside to see if they were loose or else, initially back and forth the moved very freely and felt secure, tried once mor and the perfectly flat round flap(now a disc) broke free from its position and fell too the floor.
Annoyed, I replaced the air box and the buzzing noise is still there with no change in acoustics. I will say when I ease off the throttle and gently accelerate to a higher speed the buzzing eases off.Almost as if im driving through the buzz.

Question: can any one help/advise.

Thank you.

Jason.

[nokinnikon]

As an update, i have found a new old stock (siemens) MAF sensor on fleabay for £18. Dutifully purchased. When arrives I'll fit and road test and i will return with result.(s)
If all okay i will source another airbox or cold air intake module, if possible to buy. At such uncostly small amounts its worth a gamble.

Jason

[nokinnikon]

Well I received the new MAF, all the popping, mini boy racer explosions have gone, ticks over at a rock solid 780 RPM, runs beautifully now.

The buzzing noise:

Still none the wiser, but under heavy load now, uphill in the pouring rain on busy Dual carriageway it quietened down somewhat, but when on country/normal roads same conditions and I accelerate in any gear it buzzes away again.

Any and I mean any thoughts will help

Grats

Jason

[nokinnikon]

Further update:

A complete airbox came today (£20 from flea bay) fitted bottom of box (didn't change lid top) cleaned out throttle box, flap and road tested to operating temperature and VOILA!
No buzzing sounds under load. Going to dissect the old box and see what it may have been. Hairline crack? Warping? Faulty air thermostat...who knows but the problem is now sorted.

Grats

Jason