I think I've seen stuff they actually sell that you put in before a smog check, and they advertise it as such.
I would use a good fuel cleaner, change plugs, maybe air filter, and go again....
'92 300CE - Sold
2004 C240 - C7 Wheels
2015 ML350 - P1, Pano, Ash poplar wood, Sport Dinamica interior, Running Boards Keyless go.