when to change oil/air and fuel filters?

hi y'all

just a few newbie questions

i own a Porsche 944 S2 (1989).


does the air filter have to be changed at the very same time you change the oil filter or is this matter irrelevant?

when you change the air filter do you just replace it or is one supposed to oil it first?
does the K & N air filter increase the noise of the engine?

every how long (how many miles) are you supposed to change :

the oil filter
the air filter
the fuel filter

what do you think of injector cleaners (http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=8042770834&rd=1&sspagename=STRK%3AMEWA%3AIT&rd=1)

thanks a million

Oil filter(change every oil change): For city driving or heavy usage, change every 2500-3000 miles;
For combination driving (city and highway): change every 5000 miles;
For highway-only use, some will go as far as 7500 miles, but I wouldn't recommend it.
Note: If you have run your engine hot, check your oil. If it looks cooked (or if you hear valve noise), change immediately.

Air filter: Knock it against a wall every time you change the oil, every other time, suck it out with the shop vac. If these two things don't make it look decent, change it.

Fuel filter: change it every 50,000 miles.

Oil filter(change every oil change): For city driving or heavy usage, change every 2500-3000 miles;
For combination driving (city and highway): change every 5000 miles;
For highway-only use, some will go as far as 7500 miles, but I wouldn't recommend it.
Note: If you have run your engine hot, check your oil. If it looks cooked (or if you hear valve noise), change immediately.

Air filter: Knock it against a wall every time you change the oil, every other time, suck it out with the shop vac. If these two things don't make it look decent, change it.

Fuel filter: change it every 50,000 miles.


thanks for your answer

sorry one more thing that you forgot to answer:
what do you think of injector cleaners ?(http://cgi.ebay.co.uk/ws/eBayISAPI.d...MEWA%3AIT&rd=1)

maybe i won't need them if i use a fuel filter?