hissing noise in engine bay

pedro20001 · Post by **pedro20001** » Sun 20 Nov, 2011 17:14

Evening, bit of a strange one - when turning off the engine on my 1999 2.0 there is a hissing noise from the lhs of the engine bay. it happens for a few seconds after turning off the engine. car runs fine as far as i can tell, any ideas? cheers.

Gazza · Post by **Gazza** » Sun 20 Nov, 2011 18:36

Could be the airpump, have a read here http://www.zroadster.net/forum/viewtopi ... irpump#top

pedro20001 · Post by **pedro20001** » Sun 20 Nov, 2011 19:22

sorry, a bit more info - the noise seemsa around the throttle body area but the flexi pipe seems ok at first glance although without removing it i can't rule it out. are there any other vac hoses etc that could cause this, thanks in advance

aceman · Post by **aceman** » Sun 20 Nov, 2011 19:33

OK a number of things can cause this firstly you could have an induction hose leak as they are on the left side unlike the air-pump which is on the RHS. A small split in the air intake hose usually where there is a small corrugated pipe going off to the idle control valve so check this for a split.

Secondly on the M52TU engine there is a DISA unit on the side of the inlet manifold which is basically a flap that opens to allow variable intake geometry. This is actuated via a vacuum feed and there is a rubber bung on the back of the DISA unit blocking off a port which is prone to perishing to the point it just drops off or will fall off in your hand hence will need replacing. This is also usually asociated with a slightly lumpy idle too.

Thirdly and I don't know if they were fitted to the 2.2's but if you have a flap in one of the exhaust tailpipes actuates when you revs exceed 3k then this is again vacuum actuated and there is a small air reservoir located just under the inlet manifold which charges from the engine vacuum line. It looks like a small black plastic cylinder with a couple of pipes going into it which if have a leak will emit a hissing noise for a few seconds when the engine is turned off.

Hope that helps, pretty sure it will be one of the above.

pedro20001 · Post by **pedro20001** » Sun 20 Nov, 2011 20:42

fantastic guys,really appreciate your replies. i can always count on the forum for help, now where's my torch!!!!!

DomS · Post by **DomS** » Sun 20 Nov, 2011 23:59

pedro20001 wrote:fantastic guys,really appreciate your replies. i can always count on the forum for help, now where's my torch!!!!!

In the kitchen, 2nd drawer on the left...

Frank.A · Post by **Frank.A** » Mon 21 Nov, 2011 10:43

DomS wrote:
pedro20001 wrote:fantastic guys,really appreciate your replies. i can always count on the forum for help, now where's my torch!!!!!
In the kitchen, 2nd drawer on the left...

I agree with DomS but I think the torch needs new batteries.

Z3cade · Post by **Z3cade** » Mon 21 Nov, 2011 10:51

Is there a snake under the bonnet?

sorry...

Badman gee · Post by **Badman gee** » Mon 21 Nov, 2011 10:53

Z3cade wrote:Is there a snake under the bonnet?

sorry...

good one

pedro20001 · Post by **pedro20001** » Mon 21 Nov, 2011 17:25

Sorted, was the rubber bung on the disa unit, totally split. Ironically when i checked my car, that one is split too! Nice simple fix and no more snake impressions when the engine is turned offr.

Just another quick query, posibly related to this vacuum leak - the 2.0 has the flap in the rh exhaust pipe which as far as i understand should be closed at idle. it is permanently open, any suggestions? cheers again for the quick replies and anything to save money

r37 · Post by **r37** » Mon 21 Nov, 2011 18:07

http://www.realoem.com/bmw/showparts.do ... g=18&fg=20

part 13 in that diagram is the exhaust flap ress, give the hoses a poke and see if they are cracked or have become dislodged, either that or do nothing and enjoy a better sound at low revs

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hissing noise in engine bay

hissing noise in engine bay

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