My ideas are don't mod until you've done some decent portion of the following list:
cabin air filter
all fluids--trans, diff, brake, PS, of course oil with LL-01
get codes read
clean icv/tb and replace rubber, including vac lines (see jfoj's sig)
So, those are my ideas...just for starters. Almost every car here has done all or most of the things I've listed, and if you read General forum, you'll see that there are many other items you could/should be doing before changing the way your car looks.
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Mangofy your E46!