I've got a 85 535 and this year I can't seem to pass smog for the life of me (took it in 3 times now). The reason - HC is measuring 500+ at idle (needs to be 200 Max). I do know that as soon as it comes off idle HC drop to 50ppm. They won't tell me the other gasses unless I go to an "approved" repair shop and pay $75 for an "inspection". Other than this the car runs & idles fine (~750rpm) and pulls strong across the entire RPM range.

I seem to have tried everything in the Bentley book and searched online forums and articles on the topic.

*Performed valve adjustment
*Measured fuel pressure with or w/o idle hose - in spec.
*Replaced spark plugs, cap rotor & wires
*Pulled the fuel rail and the cold start injector - works fine and no drips under pressure with fuel pump running
*Measured voltage coming from the temp sensor - in spec (cold & hot engine)
*Checked for vacuum leaks - none found and pulling dipstick drops engine RPM at idle
*Checked for binding/stuck AFM flap - all good there
*Checked 02 sensor - all good (don't know if this is measured at idle anyway, but RPM did drop when I disconnected it completely)
*Checked purge valve & hoses
*Changed oil & filter (getting desperate now)

It seems that there's something that's telling the ECU to pour in extra fuel but only at idle and I can't figure out what it is. I don't have another ECU to swap in to see if it's ECU itself.

If you have any ideas, or hunches please send them my way.

Thank you in advance,