What is the procedure for checking & adjusting mixture on my 89 260e which is set up to comply with Calif emissions? I have a digital multimeter but it has no duty-cycle function. The car failed emissions here in Az last month and the check engine light gave the fault code for the O2 sensor. I replaced the sensor approx 30k miles ago. I took it to a near-by MB independent shop ( Goody's in Scottsdale-great work & reasonable) and they set it by "feel" based on my failed readings. They were absolutely swamped and said that if it failed again to bring it in for a full diagnostic. The car passed emissions but I'm still getting the fault code for the O2 sensor. I'd like to be able to check and adjust myself . Appreciate any info anyone can offer