1991 190E 2.6 check engine light
 

Ok gang I need run down on two things first the fuse #3 had blown and I also have a check engine light. I was having a rough Idle and hesitation at begining my trips to he store or what ever, I did not have the light when checking the duty cycle, alwas good at 49 to 54%. changed plugs rotor dis. cap and new wires. No change in roughness of idle, then I found that #3 fuse was bad, changed that and it made a great improvement of idle. my question is WHY! :confused:

Check engine lamp on a FEDERAL version car happens only when the O2 sensor is inactive for 5 minutes.

Either power to O2 heater, bad O2 sensor, misadjusted mixture.

check eng. light
 

thanks MBdoc, power sorce for the ox comes from where? is it fused?

O2 sensor heater is powered from the MAS relay.

MAS relay
 

thank you doc