240D Hard Idle and almost dying out - PeachParts Mercedes-Benz Forum

JordaanDMC-12 · #1 11-18-2008, 01:29 PM

Hey everyone, I've recently been having a hard idle problem with my 1983 240D. The problem is, it will be idling fine and then it gets rougher and rougher and rougher to where it feels as if its going to die out. It got to a point to where I had to keep shifting into neutral and revving it to keep it going.

I took it in and my mechanic told me it was the piece where the hand pump is when you change a fuel filter, it was leaking Diesel and he said it was sucking in air and this was the problem. So he had it all weekend and I got her back yesterday, all of yesterday she was fine except for at night when I got a hint of it coming back. Cranked her up this morning and low and behold it was the same nightmare all over again. I did a few pumps on the fuel hand pump and fiddled with the idle to see if I could get any results.

It's not doing it now but the idle is still kind of hard. I have no idea what to look for. I'm guessing it still is getting air somehow but this is just a guess. I checked all the hoses and their not leaking. I don't know if this is vacuum related or the engine. The bigger fuel filter was changed 5 months ago and the smaller one was changed this weekend with the "repair" so I don't think that could be it. The vacuum pump was replaced about 3 months ago also.

JimSmith · #2 11-18-2008, 04:33 PM

From the description you appear to have an automatic transmission? If so, there may be an idle control other than the knob on the dash that the manual transmission unit has. If you have the knob, turn it all the way to fast idle and see if that helps. If it has no effect, the unit is out of adjustment or the cable is broken.

There is also an idle speed control throttle linkage that goes to the intake manifold and positions a throttle plate. I am not sure about what an automatic transmission might add to this device, but on a manual it can be adjusted slightly to set the low idle speed. Do a search, as I believe someone here wrote up a story on the subject. Jim

barry123400 · #3 11-18-2008, 04:54 PM

Check and adjust your valve clearances if they have not been done. What may be transpiring here is as the valves warm they elongate faster than anything else. So you have perhaps a partially open valve after warm up.

This same valve when cold and not expanded probably seals well enough to let the engine idle fine. Well worth checking if the idle is solid when the engine is cold.

curtludwig · #4 11-18-2008, 05:00 PM

Water in the fuel tank maybe?
Here on the east coast its cold enough we'll be getting condensation in the fuel tanks at night. I've added a good strong shot of a water sequestering agent to each vehicle (Seafoam in the gassers, Power Service Diesel Suppliment to the diesels) at 3 or 4x the recommended dose.

JordaanDMC-12 · #5 11-18-2008, 06:12 PM

I went back a few hours ago to the mechanic and he said he had adjusted the idling. The idle adjuster on the dash was "out of whack" as he put it and now it's actually adjustable but it still didn't fix the problem.

How do I check for the valve clearances? I'm taking the car back in tomorrow so I have all day today to play around with it.

I wish I could say I lived in an area where the water condensation could occur. Out here in "Happy Sunny Southern California"

especially in Palm Springs it's Extremely hot and dry. It's mid november and it was 90oF today with 10% humidity

I love snow, rain and severe weather and that is the opposite of where I live. Can't wait to move to San Antonio, Texas

But back to the problem, Is there a way to check for the condensation? You never know and I might as well check for it.

barry123400 · #6 11-18-2008, 06:39 PM

[QUOTE=JordaanDMC-12;2024678]I went back a few hours ago to the mechanic and he said he had adjusted the idling. The idle adjuster on the dash was "out of whack" as he put it and now it's actually adjustable but it still didn't fix the problem.

How do I check for the valve clearances? I'm taking the car back in tomorrow so I have all day today to play around with it.

Valve adjustment in the archives has step by step approaches. Basically it involves removing the valve cover and checking with a feeler gauge for the right clearances.

With time, milage, and no adjustments they tend to close or tighten up. Mercedes recommends a clearance check every fifteen thousand miles. Some of these old buggies have not been checked for a dogs age.

JordaanDMC-12 · #7 11-18-2008, 07:31 PM

Ohhhhhhh haha I'm used to just the term "Valve Adjustment", haven't heard clearances. Yeah, I had one 6 months ago when the car was purchased. He said they were all tight, which I believe because the car wasn't taken care of at all. I've been meaning to get this done again though.

I adjusted the idling higher but when I put it in drive again it goes back down pretty low. I was driving it pretty fast and it seems the faster I come to a stop it feels worse and close to stalling. I checked the new pre fuel filter and as far as i can see everything looks good. What is going on?

This came out of nowhere too, was working fine until about a week ago..

JordaanDMC-12 · #8 12-14-2008, 10:49 AM

Problem was found and fixed! I ended up needing new injectors, I'm not sure if my mechanic was kidding but he didn't sound like it when he told me he was sure I had the original injectors. He also gave me a valve adjustment and said that the valve closest to the cabin was very very tight which might have contributed to the problem. I guess when things are problem free for awhile, something has to spoil it right?

She's purring like a kitten now, and after I had the trani adjusted to shift late i'm not that slow anymore! The linkages for the accelerator pedal were adjusted also and the pedal feels normal now! no more getting stuck! Woooo

All that's left now is to replace my rear axles, replace head gasket, fix my door locks and she good to go.

leathermang · #9 12-14-2008, 02:06 PM

The standard procedure is to do the valve clearance setting with the engine cold.
You might consider replacing your engine mounts....and engine shock absorber if you have one.... these are heavy engines with rather ' tuned' soft engine mounts.. so when they get old they really let the cast iron move around.

barry123400 · #10 12-14-2008, 05:49 PM

That valve your mechanic described as very, very tight was probably the majority of your problem. As the engine warmed up the valve no longer sealed properly so you probably had the fourth cylinder dropping out.

Injectors do not usually go downhill as soon as the engine warms. So what was wrong is more dependant on what he did first.

If he adjusted the valves and engine still ran marginal when warmed a little it probably needed the injectors. My bet is he did the injectors first and the engine was still rough as soon as it warmed a little. Then he adjusted the valves and the engine cleared up.

It really pays to do your own service on your cars when possible. In your case the injectors may not have been in good shape. If they have been substantially improved you should now see better fuel milage than you had before this problem occured. If fuel milage is identical then the injectors might have been just fine. .