My polo has developed reduced power - it runs as though it isn't getting enough of something - very noticeable uphill - second gear only to make the last hill home and that is a real struggle. It doesn't want to go over around 3500 revs but will when not in gear.
It also is making a hissing noise which increases with the revs - it is a definite hiss not wind. The hiss seems to be coming from the side/s of the car - its really odd - when you put your head in the engine bay you can't hear it.
Lastly it takes ages to start in the morning, it struggles to run and then is fine - and will be for the rest of the day.
Could there be one unifying fault?
Changed plugs, Changed HT leads, Changed air filter, Cleaned throttle body.