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Hissing noise and sluggish acceleration


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Hey guys and girls...

I'm considerably stumped with this one given the number of other posts around the net regarding very similar issues.  The car is a Ford Mondeo Mk 3 - 1.8 Petrol 2004 manual.

There is a loud hissing noise coming from the engine towards the front; it appears to be coming from the area to the left of the air filter although doesn't appear to be the air filter itself.  I have taken a video of this which can be seen at https://www.youtube.com/watch?v=1UwU-6KO-TE.  I've attached some images to the post detailing the general area that it can be heard around - I have also labelled a pipe that was directly in the loudest sounding area although I have no experience with this hence my lack of knowledge.  I  hovered with my ear around the area marked and the noise is very clearly heard.

The effects on driving can be seen at https://www.youtube.com/watch?v=eLfo67fkvMk (my foot was flat to the floor for the full duration of the video with the car in 3rd gear) - the car will rev without any problems when not in gear although when driving, the revs are very slow to pick up and eventually stop increasing around 5000.  If I push the pedal to the floor in a slight gradient, it will start to loose revs fairly quickly.  The engine responds fine to acceleration up to around 3000 RMP. 

Around 3 months ago I had very similar problems with acceleration and had run the car very low on fuel for a while.  I filled the tank up and used a good amount of fuel injector cleaner (wasn't redex but very similar).  Shortly after, the engine sputtered at around 4000 and the revs suddenly picked up as if there was nothing wrong and had run fine since.  I've tried that again although this has made no difference.

After some research, I now believe the problem to be related to the hissing noise and this may have just been a coincidence.

I have no knowledge of the engine so I am at a complete loss and have no idea where else to go - I can't afford to take it into a garage or replace semi-random parts at least until I know roughly what the problem is.  I have ensured oil is topped up as recommended by a friend and have cleaned (although not replaced) the air filter,  The hissing noise has been getting steadily worse.  I can't see or feel any splits although suspect I have simply missed it.  A brief spray of lighter gas around the area didn't produce anything to work with although I was very hesitant so may not have used enough or in the right area.

If anybody has insights into what is causing the behavior and if the hissing and poor performance are actually related, I would really appreciate your advice.  Let me know if more information is needed and I'll do my best.


Kindest regards






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i take it your brakes work fine , as what your circling is the brake booster vacuum line. does it tick over at normal idle around 750rpm?

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from what your describing in your post it sounds like intake manifold runner has broken up, sucking air in giving hissing noise, with poor performace due to manifold runnrr flaps staying closed blocking air flow under higher load. or it could even be the vacuum pipe to the actuater ( for the operation of the flap) split hissing and stopping operation.

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