In Reply to: Black Soot on rear bumper = bad AFM????? posted by Erik Brannfors - Seattle M3 on June 01, 2002 at 12:02:08:
Usually though, CO only needs to be adjusted at idle w/ car at normal operating temps. This is the first item to have done to solve this problem.
If AFM cannot adjust CO down then AFM is bad.You want to try and adjust the idle bypass screw under that cap you refer to on the AFM. Also, the AFM swep needle which corresponds to the flapper position will wear out the second contact point rendering the AFM useless.
If you cannot get CO down to .85% down stream w/ O2 sensor disconnected then another item may be contributing besides the AFM.
DO NOT ADJUST THE IDLE BYPASS UNLESS YOU ARE CONNECTED TO A GAS ANALYZER TO MONITOR CO LEVELS!
IF you get CO adjusted to proper levels then connect the O2 sensor and see if CO & CO2 levels change.This will indicate a properly working O2 sensor too.
May as well get t-bodies synched and base idle set too!