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Old 01-07-2003, 07:31 PM
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Join Date: Sep 2001
Location: Vancouver, B.C.
Posts: 19
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?


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Old 01-08-2003, 11:24 AM
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Join Date: Jul 2002
Location: Trenton, NJ
Posts: 248

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.


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

'87 560SEL 267K (177K on motor) Blue/Blue
'98 Buick LeSebre 60K (wife's car)
'56 Imperial Sedan 124K
Past Cars:
'67 Dodge Monaco 130K (Sold)
'87 Chrysler 5th Ave 245K and going strong (sold)
'73 Plymouth Satillite 175K (sold)
'96 Chrysler LHS 80K (totaled)
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Old 01-08-2003, 11:36 AM
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Join Date: Feb 2001
Posts: 19
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.
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Old 01-09-2003, 06:41 PM
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Join Date: Sep 2001
Location: Vancouver, B.C.
Posts: 19
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.
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Old 01-09-2003, 08:03 PM
Super Moderator
Join Date: Apr 2000
Location: Falls Church, VA
Posts: 5,316
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.
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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Old 01-10-2003, 08:10 AM
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Join Date: Nov 2001
Location: North Central Kentucky
Posts: 1,068
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"

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