Volkswagen: My car seems to loose some power, shell optimax, fuel system treatment

Question
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Followup To
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 -
why was the fuel additive added? what size engine? 8v or 16v? i need to know the above info so that i can give you any advice i possibly can regarding a remedy.

Hi thanks for your reply. My engine is a multi-point injection 999cc 50bhp 8V.
There wasn't any particular reason for adding the fuel additive, just to keep the fuel system clean.

Thanks

Regards

Matthew Abela  

Answer
it may be the additive's in the slick 50, i would suggest running the car virtually empty then filling it with shell optimax or similar fuel. due to it's higher octane rating, the car tends to feel a little more responsive and also the fuel burns cleaner. (i have a 16 year old golf gti with multi point injection, when changing my plugs the last time, the pistons where dull grey. when i aquired the vehicle i did the plugs and the engine was full of carbon. so it seems that it really does help to keep it clean as it cleaned 100,000 miles of carbon out of mine in just 15,000 miles.) i use optimax every other tank full as a general rule.