performance is great some days, but only good others?

[Korndogg]

hey all
just curious about something.. sometimes my car will run really really fast, and others it will be somewhat sluggish... and i don't understand why. it doesn't appear to be temp or humidity related, so i was wondering what mechanically could account for this?
also, it almost always runs very well after i've been on the interstate for 45-60 mins.... *shrug*

i was thinking that i should replace the (front) oxygen sensor, change the fuel filter, and perhaps a new PCV valve.

does anyone else think that any of these could have to do with the weird performance variation?
anybody have any other suggestions?




sidenote:
also, for anyone who read my recent post about a little blue smoke from the exhaust.. i changed from mobile 1 10-w30 synthetic to mobile 10-w30 mineral oil and the blue smoke is gone, but now my exhaust smells a lot worse from the lack of a cat. and after 50 miles, i got a CEL for the cat. so now i gotta pull that o2 sensor.



stats on car:
1996 TSI FWD
2.5" catback with punched stock cat
K&N FIPK
boost @ 17psi
new plugs (bpr6es) and wires (NGK)

i think that's all...

thanks everyone


edit:
oh yeah... i've checked recently and there's NO play to the turbo at all... none


edit2:
also... doesn't that ^^^ suggest that synthetic oil burns cleaner than mineral oil?
i didn't know that that was one of its benefits *shrug*

 

[Korndogg]

no one even has any comments about my current ideas to possibly fix the problem? does it seem possible to anyone that it could be the oxygen sensor, fuel filter, or PCV valve? (i figured PCV while i'm at it because it's so cheap 'n' easy)

thanks

 

[Korndogg]

it didn't smoke at idle... it was sort of random.. buti could get it to smoke some if i reved the engine real high for a few seconds and let it come back down.. it would then smoke a bit after coming down.. but anyway.. that's beside the point

yes, temperature does make a difference on my car... but my question is about the fact that it also fluctuates performance-wise regaurdless of temperature... some hot and humid days it will run like a mofo and i don't understand why?.. i've been paying attentino to it.. and yes, of course it runs better in GENERAL when it's cold and dry out... but sometimes it will run fast when it's a certain temp, adn sometimes not...

that's more of my question..... what causes it to fluctuate even when temp remains solid

thanks