I bought this Black on Black 560sel that had a head replacement that blew a gasket. I had an extra 560 so I swaped it (just the long block). I put in a new O2 sensor and water temp sensor. The car starts and runs good until it is up to running temp. Then it drops the idle from 10K to about 700 RPM and will not move up from 700. During this period, the engine light does not come on. If I unplug the O2 sensor, The engine light comes on and it runs just fine except for a high idle and probably bad fuel economy. I have herd of this happening to other good running Mercedes all of a sudden but I can't find anything in our forum that documents this problem or a root cause. The online manual I use is unclear as to how I can check my O2 sensor. Does anyone have any insight before I start throwing parts at it?

Pull the warm up regulator and see if it's full of crud.

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600SEL '91
300E 4Matic '88
240D '83
280SE '77
350SE '73
The most complex systems can fail in the simplest way.
Contra verbosus noli contendere verbis, sermo datur cunctis, animi sapientia paucis.

i don't believe in the lord! He's never bought me a Mercedes Benz.

I didn't have a problem with the cold idle it was the hot off idle. I don't get gas to my injectors when its warmed up. The fuel pressure is good. I installed an electric fuel pressure gage.

No WUR on the US 560s.



Your new parts could be bad. Test them per the manual. O2 readings should fluctuate once the sensor is warmed up

So it will not rev past 700rpm?

Have you checked/set the CO?

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I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

The manual is ambiguos as to which wire is to be hooked up. It just shows a test lead leading to the duplex connector. Also, what is the WUR and CO? That is what I thought also that it could be bad but I get no engine light. Thanks for the input.

WUR is warm up regulator. Only the 1985 MY and older US W126 V8s have this.

CO is carbon monoxide. This is the adjustment on the CIS tower, it is a VERY fine adjustment of the flapper plate.

Did you ever drive the car with the donor motor?

The temp sensors are usually NTC. They will have say, high resistance at cold temps; low resistance at high temps. Just try another sensor.

Any vacuum leaks on the thing?



Read this: BOSCH KE3-JETRONIC MIXTURE ADJUSTMENT

__________________
I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

My understanding is the CIS adjustment is a fine adjust. When the engine is warmed, a push to the gas pedal will open the flapper plate and the engine will die. I never drove the doner car. It was not running when I got it. The old guy that owned the 350SL had replaced the 450 with a 560 from an SEL. He had a heart problem while halph way through a paint job and needed to get rid of it. My temp sensor was the last new part I bought from Phil before he died.

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Until you test parts, there is nothing further I can offer for help.

__________________
I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

I'l try to test the O2 sensor this Saturday.