Gremlins? 98 E300 - idles rough until lights are turned on

[SRHeer]

My 98 Mercedes E300TD is acting weird
I have one check eng code for a fuel shutoff valve as it doesn't turn off right away but revs up for a bit then shuts down - part ordered
Now the weird thing is that while running with the lights on it idles perfectly
But when I turn the main light beams off idle gets rough as if it is missing or something???

[JHZR2]

Sounds like a short or issue that affects some controller.

Are you sure your glow relay works right, and keeps the afterglow on during a cold start? Are you sure all glow plugs are good?

[SRHeer]

all my glow plugs measure .6 ohms resistance - I don't know how to check for after glow - put a meter in parallel while its running? it misses even after it warms up unless I turn lights on

[SRHeer]

[QUOTE=JHZR2;4228437]Sounds like a short or issue that affects some controller.

Well with lights off no voltage is going through circuit which would be an open but how could an open cause rough idle? unless there is bleed through somewhere when it supposed to be open or off?

[JHZR2]

Originally Posted by SRHeer

all my glow plugs measure .6 ohms resistance - I don't know how to check for after glow - put a meter in parallel while its running? it misses after it warms up unless I turn lights on

Afterglow would probably be easiest measured by a clamp on ammeter on the GP relay main wire. Not everyone has one, and I know in the older cars and my Cummins trucks you can see if the heaters/plugs are on by the alternator voltage staying artificially low…

That said, the fact that it does this after warming up would tell me that it has more to do with the electric control. I’m not immediately familiar with the differences in electric diesel control and idle control in a 98 OM606 versus my 602/603 cars. What I know is that my 93 300sd which starts and runs beautifully will have an oscillating rpm when I use the turn signals. I can feel and hear it, and see the tech changing.

At least on the 693, the base idle can also be changed through a screw. Upping that helped my engine nicely. EDC/ELR still keeps it at the right rpm and allows the act to work and whatnot. So you should check if the 606 can have a base idle adjustment on the IP. Low base idle with an electric glitch could be a reasonable cause.

[SRHeer]

Found my problem to be leaky delivery valve seals - had changed out two of the fuel SOV and replaced all seals on fuel lines - noticed no air in lines with engine off but while running little bubbles of air streaming through fuel lines - also now when I step on accelerator it actually puts me back a bit in seat!