Smoke coming from 94 acura LS

I have a 94 Acura ledgend LS that i'm quite fond of. Lately i have noticed that when i'm stopped in traffic for a while and then i take off Smoke is
coming from my tail pipe. What is the likley cause of this. I have noticed other acuras around the 93 or 94 models that are doing the same thing. I recently changed the PCV valve but that didn't help. Is There some kind of safe additive that i can use to help eleviate this problem?
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