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Old 06-02-2013, 05:56 PM
Harrison W's Avatar
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Join Date: Feb 2011
Location: Boise, ID
Posts: 68
Odd OM603 Low Idle Issue

Ok, so here is the story. I started the car up drove it about half a mile, shut it down. I then drove it about another half of a mile, shut it down. The next time I started the car it started to idle at only 400-500 RPM's. No smoke, no blow-by, oil level is fine, and the car has plenty of power. Besides this idle issue the car drives perfectly. I did run around 40 or so gallons of Biodiesel through the engine over the last 2 months, maybe this could be a cause...?

I changed the fuel filters yesterday with no change in any of the symptoms. Also, changing the ELR also does nothing. Here is the video I took this morning of the engine running at idle. I hope it helps to diagnose this problem.

OM603 Idle - YouTube

What could be causing this? Any help or insight would be awesome.


1987 300SDL 271,000
1999 E300 Turbodiesel 155,000ish. (Dad's)
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Old 06-02-2013, 06:36 PM
Jeremy5848's Avatar
Registered Biodiesel User
Join Date: Mar 2006
Location: Sonoma Wine Country
Posts: 8,401
The EDS system is not working correctly. One of EDS's jobs is to run ELR. Since the tach works, the signal from the sensor at the flywheel is generating a signal, the signal is getting to EDS, and then is getting sent along to the tach. This also says that the OVP relay is working. Your a/c (assuming it's otherwise in good shape) should also work (Klima requires the tach signal or it won't allow the compressor to engage).

The EDS electronics are generally very reliable. I'd look for a broken wire or a damaged or loose connector. Remove and reseat the EDS electronics (behind the battery). Check the wiring and the connector at the red circular thing on the back of the IP as well as the plug and the wiring at the throttle position sensor (TPS) on the right side of the IP. These may be hard to see with the intake manifold in place. Use a flashlight and a mirror. See the photo.

Thanks for posting the video -- very helpful.


The biodiesel should make no difference unless you spilled a lot of it and it dissolved the insulation on a cable -- unlikely.
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Odd OM603 Low Idle Issue-ip_6557a.jpg  

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Last edited by Jeremy5848; 06-02-2013 at 06:41 PM. Reason: Add photo
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Old 06-03-2013, 06:12 AM
Registered User
Join Date: Oct 2006
Location: Beachwood, NJ
Posts: 462
Consider adjusting the base idle at the injection pump higher.


1987 300SDL
1991 300SL
1990 560SEL
2001 ML320

1969 200D 1979-82
1983 300SD 1984-85
1972 250C 1982-02
1995 S350 2011
1997 S320 2012
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