running rich

[Rixmax1992]

Hello everyone: I have a 1991 Q45 no longer an a with 223K. I changed my plugs today with NGK platinum lazer cut. When I pulled the old plugs out they're gas fouled. I recently tried to get it smogged but it failed due to hydrocarbons. I tried the trick getting the cats red hot but that didn't work this time. The smog technician said since I was close to passing try and put some new plugs in. Should I adjust the idle mixture. RixMax

[3Q Jay]

you can't adjust the idle mixture.
you could have intake air leaks which would cause the STFT to read lean and therefore the ECU would call rich.
check your O2s, check both STFT and LTFT.
what did your NOx read?
hell, post up your report if you can.

[Q451990]

I learnd'd something... STFT = short term fuel trim.