1992 W124 230 TE rough idle

jibcl500

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CL500,ML55,SLK280
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just bought a 92 w124 230 te, the idle is rough, the engine will rev to 1100 rpm and hold then drop to almost a stall then back to 1100 rpm.
If I blip the throttle to 3000rpm and release the revs drop but hold at 2000, 1500 rpm etc then down to a steady idel.
If I select D the revs drop slightly down to 500-600 rpm.

Ive cleaned the idle control valve, replaced the plug also as the wires where exposed.
Disconnected the cold start valve no change.
checked all breathers and vac pipes all good.

Any other thoughts please.

jib
 

meanie

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Is the breather filter in the top of the rocker cover blocked? Can cause an odd idle sometimes.
Check the voltage to the idle valve with an an old fashioned analogue multi meter, it's a lot easier to see if the rev anomalies correspend to voltage change.
Sticky or incorrectly adjusted throttle switch.
Poor earth .
Fuel pressure control fault.
That said, most likely cause is a tired idle control valve.
 

The Crooner

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2006 R320 cdi
First thing to check is the OVP relay - if that is not working correctly and consistently you will never get it to idle right.

Then its all the sensors, starting with the dual ignition/FI temperature sensor.

Then the idle switch at the front of the throttle cable.

And yes some good cleaner on the idle control valve - if its free you can hear the internal flap move when you shake it.

Good look - you might want to search through my past threads for more info. Mine is now rock steady at 750rpm.

Tony
 


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