rough idle at stops when hot- om601
 

Hi All,
does anyone have an explanation for why Benz diesels tend to idle rough at stops, when hot?

I'm sure many of you have noticed your oil pressure dropping at stops, which can freak out many new drivers who aren't used to it.

My 190D 2.2L (om601 engine) has always idled poorly at stops when hot, and it has gotten worse to the point that I sometimes think she might stall. I've tightened up the throttle cable a little, which has helped.

She is well-maintained at 240K miles, with rebuilt injectors and a cooling system that is performing well (to the best of my knowledge). Temp gauge recently stopped working :-(

Can anyone explain why diesels behave this way when hot?

Thanks!

Properly sorted MB Diesels don't behave that way. If your engine has EDS, maybe there's an electrical fault in the idle control system. Otherwise your engine might have a solenoid that kicks up idle under certain conditions. Is base idle speed properly set on the IP? Are your engine mounts in good shape?

http://www.w124performance.com/image...ne_mounts4.jpg

Oil pressure as low as 1 bar or 15 psi at idle generally isn't a concern.

Sixto
83 300SD

Thanks Sixto for your reply!
my 1984 190d doesn't have the hydraulic engine mounts, just the solid rubber ones and they have been replaced last year. Thanks though for including the diagram.

The vibration of the lower idle at stops isn't as much of a concern to me as the lower idle speed itself. Before tightening up the throttle cable, it stalled at least once at a stop. It is better now, but still feels iffy.

I will take a look at my repair manual to learn about adjusting the IP's idle and the presence/ location of a solenoid to regulate idle, unless you have a reference...

What is EDS?

Thanks!

I think you may have electronic idle control identified by a silver dollar size actuator mounted on the rear of your IP it also has a 2 wire connector. That is powered from your overvoltage protection relay I would check that first.

my om 617.951 does that unless I drive it hard for a few miles.

EDS = electronic Diesel system, MB's system that on '80s Diesels takes care of idle speed and emissions. 602s and 603s have it. I don't know about 601s.

Sixto
83 300SD

Say again?

Dieselbenz1,
thanks for the hint! I can see at the rear of my pump a two-pronged electrical connection which is filthy from never being connected. For the life of me, I cannot find any unconnected wire which should be plugged there.

Do you know where these leads would originate from, or how to find them in the engine bay?

My 190d is 1984 (the first year) and all the diagrams I can find of the IP show a vacuum pot in these location, not an electrical connection. I wonder if my IP was replaced at some point....
but then again, I don't have any un-connected vacuum connectors either. Wierd.

Thanks All!