Volkswagen: My cars seems to loose engine power, fuel system treatment, ignorant definition

Question
VW polo (October 1997) petrol   

I noticed this problem after that I added a fuel system treatment (slick 50) to the tank, and my mechanic replaced the fuel filter, 2 days ago.
 I can say the engine didn't loose that much performance. What i noticed very strange is when the car is idle and i press the gas pedal, there is a slight delay in engine response and u can actually hear some sort of valve opening.

Thanks for any help

Regards
Matthew

Answer
Matthew:

Let your tank run down close to empty, and place another new fuel filter in your Polo. (again).

If it is available in your region,  get "Valvoline Fuel Injection Cleaner" it costs about 9.00 USD.   Don't get a 2.00/3.00 USD knock-off as it does not have the same cleaning properties.

Pour the entire bottle (you can even use 2) into your almost-empty tank.  Fill it with 93 RON (recommended octane rating) or higher fuel/petrol.

You should be fine.  

Don't use the Slick 50 in your fuel.

(You said "Petrol", I am assuming you are talking about a non-diesel fuel).  

If your car IS diesel, IGNORE the above procedure,  write me back and I'll help you out ASAP. (Sorry for my ignorant definition of "Petrol"!)

Thanks,

Ron