I used a bottle of Good to Pass (GTP) bought from a local auto store and a tune-up. Before getting the smog check, I drove for twenty minutes on the freeway and when I was waiting in line for my turn, I left the engine running.

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200 75 W115 (Mom's)
190e 90 2.6 W201
E320 95 Wagon W124
72 BMW 3.0 CSI