You have an OBD1 system (last year for OBD1 in the US was the 1995 model/year). You can buy a computer chip that replaces the factory chip that will change the fuel mapping and ignition advance curve. They can be as cheap as ~$30 for an eBay generic performance cloned chip to several hundred for a custom designed and burned chip made specifically for your car and any mods you have made to the engine (headers, CAI, cams, etc.). Turner Motorsports and Dinan are two companies that make custom tuned chips. There are many more. In your case, you need to make sure the chip is certified by your nanny state's California Air Research Board.
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Quotes to live by:
guessing gets expensive
nothing is more expensive than a cheap BMW
Ken Kanne, Silverhill, AL, Honorary Forum Grandpa/Craigslist addict/Hoarder of all sorts of stuff
1995 318is "Bebe"; 1993 325is "Elvira" 1985 635CSi "Katja" 1984 633CSi "Sylvia"
I NEED A NAP, DANG IT!