560SEL, O2 Sensor light, rough idle
 

Ive got an '86 560SEL. It's had rough idle since I bouhgt it . I paid for some diagnostics at the dealer's and they suggested new injectors. I changed them, the car ran better, started much better and the idle improved.

Then the Oxygen sensor light came on. I figured it was time to change the sensor anyway. I got a new one put in. Now the idle is much rougher than ever AND the sensor light is still on. Any ideas?

Thanks

Martin,

I've been down a similar road with my '87. The only other rather simple thing that I can suggest that you didn't mention but probably already checked is the plugs, wires, and cap and rotor. My own experience suggests that these may be a major part of your problem.

Other areas to consider would be the fuel distributor and its associated controls. Unfortunately (for you), I've had no problems with these and therefore can't offer any advice. There is a lot of information in the archieves on these subjects however.

jlc

PS If I've done my math right, this should be my 100th post and should make me a Senior Member :cool:

New injectors can affect the fuel mixture or lambda adjustment, you need to make sure lambda is correct before doing anything else to this car.

Thanks for the Lambda suggestion. I will get my mechanic onto it. The curious thing was that it was changing the O2 sensor that made things really bad. Replacing the fuel distributor is the first thing we tried, way back when, and nothing changed. Any idea of why the O2 sensor light is on permanently?

I'm genuinely puzzled.

On my 107 wiring diagram, the O2 warning light is connected to the speedometer! No connection to the sensor or EMS.

Dunno why the new O2 sensor made things worse.

I think the O2 light is strictly a reminder that goes off at a preset number of miles--probably an EPA thing. Sounds like what happened is that you had a good running car, the light came on so you tried to do proper maintenance, then someone installed a new sensor and in the process, screwed up the car. Could be:a bad sensor, a bad connection at or near the sensor (always pull apart the connector and see if the pins have moved or gone bad), a wire broke due to age/stress form working in area. Did you put in a factory sensor or an after market? Did it come with the proper connector? You tried to do the right thing. Unfortunately, "no good deed goes unpunished"