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sucking noise around throttle body?

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Lupo 1litre petrol. 2004. 

Today I changed the timing belt on my lupo. To do this I had to lift up the air filter box to get to engine mount bolts and top part of timing belt cover.

It's all back together now and running but when i touch the throttle pedal I get about one second of sucking noise as the revs rise. If I jab the throttle the sucking noise is accompanied by the engine faltering before the revs rise.

It seems to drive ok but I do hear the suck when I put my foot back on the throttle when I change up gears, only for a second each time.

I have since removed the air filter box twice and checked everything (the pipes I took off and put back on when working on car were one thick one on drivers side of air filter box, this has a horizontal attachment. And two narrow ones on passenger side of air filter box with vertical attachments.)

The only thing I can think is wrong is where the air filter box goes onto the throttle body. It is impossible to see this go on, but I am sure it is fitted correctly. Is there supposed to be some kind of rubber seal here? is this a known problem area? 

 

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isn't the rubber seal for the tb attached to the air box base?

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yes there is a rubber seal there. I did not realise the separate seal was there, I thought that was part of the plastic air box moulding. I have removed seal and checked it and it seems ok. I can't find anything else wrong. The brake servo pipe is good . As far as I can tell the seal where the servo pipe joiner goes into servo is good. 

With air box off I can't really tell due to sucking from throttle body intake.  with air box on you can't get to anything or see anything. 

But the thing is whatever you do with the throttle you can't keep the sicking noise there, it is just for a second, more light a 1 second chuff of sucking. 

Never did this before I changed timing belt, it must be something to do with me removing the air box and refitting it. all vaccuum pipes checked for splits and ends on properly.

Got my wife to reluctantly sit in car and keep jabbing throttle to make the sucking noise while I had me head under bonnet. All I can say is it sounds like it is somewhere under the airbox. 

Does not really affect driving of the car, but very annoying noise and I don't know if it will adversely affect the emissions at MOT in August

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took it all off again and still can't find what's wrong. But I did achieve something, I found the bulkhead grommet for the clutch cable was not fitted properly. Now I have fitted that properly, I do not hear a big chuff inside he car when I change gear.  Out of ear shot, out of mind

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It could be that the throttle body is sucking in air when you accelerate, sounds like new engine time... 

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4 minutes ago, cj1 said:

It could be that the throttle body is sucking in air when you accelerate, sounds like new engine time... 

Lol.... Bit extreme.

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stick some pipe in your ear and see if you can narrow it down (with the other end of the pipe, not just having pipe in your ear as some sort of talisman).

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"stick some pipe in your ear".  I had not thought of that. It's the sort of thing I would have done 30 years ago when I was doing a lot more work on cars, but I am a bit out of practice and forgotten a lot of these methods. perhaps I'll have a go at the weekend

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