sudden onset of rough idle 240D
 

My 240D suddenly developed a very rough idle. I had been using Power Service fuel additive but had stopped so I thought maybe that the injectors had become fouled. I used some fuel additive thinking that it might clear things up, but it had no effect.
Engine runs OK at speed, a little rough, ( rougher than before) but not real bad.
I adjusted the valves today, but with no discernible effect. It seems that there are brief ( 1/2 second to 1 second) periods when the idle smooths out, but then its rough again. I checked the EGR valve, and when I applied vacuum to the EGR, the idle got rougher and there was more noise from the intake, so I assume that is not sticking in the open position.
Could it be air in the fuel from a leak somewhere in the system? I want to replace the clear fuel lines but could not get any today.
Any ideas on the cause of the rough idle?
Michael
Bel Air, MD

I had a similar problem once with my 'ol '81 240D. I could not find any fuel leaks yet the engine was idling poorly. I took it to an independent mechanic because i could not figure out what was going on. Turned out the primer pump was bad. He replaced it and no more rough idle. Another thing that i can think of is that you might have gotten a bad tank of diesel at the last fill up.

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I thought maybe air was getting into the fuel system, so I replaced the claer lines with vinyl tubing, temporarily. No bubbles were observed.
It also smokes at idle which it did not do before.
Does it sound like it just got to the point of being too worm out?
Michael Fowler

Michael
I would crack an injector line one at a time and try and find out which cylinder it is. Then swap the injector and see if the bad cylinder follows the injector. When its warmed up is it still rough?

Thanks Stevo,
I did as you suggested and all injectors slowed the idle about the same; no perceptible differences.

The idea is to see which cracked injector nut causes the odd noises to stop, not which one slows the idle. When cracking the nut stops the odd noises you have found probably found the faulty injector.

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previos to the start of this problem, the 240D would accelerate ( albeit, slowly) right up to the high end of the speedometr, and a little beyond---90 mph or so.
Yesterday, the best I could get was 75mph.
Later in the day, the power dropped again, it barely accerates to 50 now.
I noticed no symtoms that accompany the power loss. No could, sputter, no noise, no grinding, nothing. I am beginning to suspect the timing ( valve or pump) has slipped, but no noises accompanied the power loss. I hope to pull the valve cover and check the timing marks.
Is it possible that the injectors are the problem?

Howdy,

I might suggest a fuel filter or clogging problem. If you use a fuel conditioner it might have knocked some crud loose.

Sholin
(190D 2.2)

"I am beginning to suspect the timing ( valve or pump) has slipped,"

Not real likely unless its been messed with. I would agree that your high end loss of power is filters, but that usually wouldn't effect your idle, unless there really bad then it wouldn't accelerate at all. You say when you crack the injector lines one at a time you cant figure which cylinder is giving you an idle problem ?

Steve

AIr filter
 

This sounds like you are strangling the motor for lack of air.
Everyone is talking about air in fuel, but you also need air in cylinders.
Remove the air cleaner and see if the idle improves.
Otherwise, I suggest, like others, that you may have a bad batch of fuel.