rough idle for first 2 minutes until oil is warm.
 

I have noticed that my idle is really, really, really rough. The entire car is shaking violently until the oil temp gauge reads about 60 C. After that, it seems to idle pretty smoothly. Not perfect, but it is very very tolerable (especially when the idle adjust knob is all the way up). Starting the car is always great, and it starts in less than a second (always).

Is this a symptom of possibly bad glow plugs. I did an electric 12v test and all the glow plugs are getting power. But it could be possible carbon buildup in the pre chamber or one or more of the plugs may have gone bad.

I guess i am trying to see if this is more likely the problem... or i should probably do a compression test as this symptom (really rough until warm) is usually a compression issue?

Just trying to narrow down my possible problems. I don't think it would be the motor mounts as it would probably not nicely level out at a warmer engine? (yes i did a valve adjustment)

could the injectors be causing this?

-Thanks!

got smoke out the back? my guess is glow plugs, one of the pros should be along shortly

no smoke in the back. But it is really rough until warm. Worried it could be compression, but the fact that the idle smooths out after the oil gets warmer could be a good sign. Also, it always starts really really fast. Never a 4-5 second start/tries. Always boots up in less than a sec (albeit really really nasty rough for those first few minutes.. not like its dying our coughing.. but just shaking and vibrating).

There is no oil temp gauge. You have coolant temp and oil pressure gauges.

What car is it, first of all?

I meant coolant temp.

1982 240d, manual trans.
Oil pressure is always at 3 or closr to 3. Never at any point in driving does it get below 2.5

Pull the glowplugs and check them manually. Bad motor mounts will also amplify vibration, which would be most noticeable when cold. If you valves hadn't been done in a ling time prior to your adjustment you may need to do them several times over the next 1000 miles or so before they hold their adjustment.

If a glow plug tip or two is burned off you will get a rough cold idle. While the engine is running the glow plug is a hot spot to help ignite fuel even though it isn't connected to electricity.

An injector that is drizzling fuel will run rough cold also.

but the fact that it smooths out is a good sign in terms of bad compression? I should probably do a compression test although i don't have the gear to do it. I guess it is also partially the fact that i am somewhat scared if the compression is bad.. as well all know.. the engine is kind of toast until a rebuild with bad compression( don't half ass it i guess).

Anyways i will check the glow plugs next weekend and it is more than possible an injector has gone bad.

Is there a good way to test the injectors?

Test your glow plugs first, check glow plug fuse, best to replace the fuse just because. They get tiny hairline cracks that are hard to see, get a few extra they are cheap.

Don't forget to ream out the glow plug holes, go easy!! Blow out the soot with compressed air
DONT FORCE the reamer.(sorry this info is wrong, dont use compressed air, some type of grease
Is supposed to be used instead)). Search proper proceedure or someone will chime in with proper insrtructions....)

If you have the old style pencil glowplugs there is a mod to the newer style. Not sure what your model uses. But good glow plugs make start up easy and smooth. Probably havnt been changed in years, worth doing. Dont use autolite. I think bosch is the right brand

Usually these old cars just need the basics done to them and they run great.

They usually sit unused for years cause the previous owner didnt know anything about diesel.
Thats how I aquired mine :) Ran aweful till the basics were done. Now its great!

Get fresh fuel, clean the fuel sender, fresh filters, change the oil, flush the green coolant out and use the right stuff, you have a manual so you dont need to flush tranny.. ;) Air filter housing usually needs new bumpers under the housing on the mount, they get rattled to death!!

Dont jump to conclusions just yet. Basics first, then the pros can get you in the right direction with the nozzels and ip, compression and all that good stuff

Go into your profile and add in your signature your model and that its a manual 4 speed (looks like it was either and engine swap or 4 speed swap?)
That will help for your future posts, so everyone wont have to keep asking year/model
Lots of different changes over the years and these guys know just about everything about every model

youtube has a bunch of videos about mb diesel engines

Compression Test: the best compression test is a cold start. As long as your engine starts fine, don't worry about compression. Low compression can have many causes, and many of them can be fixed by proper maintenance, proper engine oil (Mobil 1 has mild cleaning properties and may help free stuck rings), proper driving habits, and proper engine hygiene habits (hint: don't let your car sit and idle, either to warm up or for any other reason if you can avoid it).

Seriously, don't go looking for problems. I was much like you with my first diesel Benz, and I really wanted to fix the car right and get everything perfect. The issue is that we have a tendency to jump to conclusions without enough data and facts. I was additionally hampered because all my automotive knowledge was based on gassers, and a diesel engine is very very different.

Rough idle: glow plugs, then injectors, then injection pump delivery valves. This order is from most likely to least likely. Research glow plugs, learn how to test the type of glow plugs you have in your car, and test them. I recommend you start a new post when you run into trouble with testing / diagnosing your pre-glow system.

+1

Yes, you need an injector tester to measure the opening pressure and a glass container to discharge the injector into so you can observe the pattern.

If you only have one or two that are suspicious, you can move them to another cylinder (don't forget to use a new heat shield under each injector, they are one-time-use items) and see if the problem follows to the new location. If the problem follows, then you can be pretty sure you've got a bad injector.

Most of us don't have those ($$), so we take our injectors to a local Bosch shop or independent MB garage that has the tester and an expert to use it, and pay about $10 to $20 per injector to have them cleaned and tested and get the opening pressures set to spec.

If you really want them done right, contact Greazzer on this forum and he'll set you up, but you'll have to ship your injectors to him and then not have a car to drive until they get back, or buy a set from him (if he's got some in stock) or buy a set to run in your car while your injectors go to Greazzer.

thanks for all the help guys. I will start with changing/testing the glow plugs next weekend. I tested the relay and power is getting to each plug. A plug could obviously be burnt out or too much carbon buildup and i will start with that (and then move onto injectors).

it is good to hear that if the engine starts up fine then it less likely a compression issue. If the glow plugs do not fix the problem, i will move onto the injectors next!

Thanks everyone!

ok an update.

replaced all the filters(pre, main, air, tank), flushed all fluids, did 1.5 L of diesel purge.

I then replaced all 4 glow plugs and reamed out the glow plug holes as stated. I also replaced the glow plug relay too.

The engine still runs rough when cold and shakes very very violently when cold still. After 1-2 minutes it smooths out ok... probably still a little too shaky... but for sure not too terrible (i know they are supposed to rumble a bit).

If i turn the idle adjust knob all the way down (low rpm) it shakes very very violently and sometimes will even quit if the engine is cold enough (not sure if that helps with the diagnosis).

When driving at speed it is fine and no issues.

I am thinking about doing another valve adjustment... but should the injectors be next? Is there a way to just unplug one injector and run the car on 3 cylinders? (see if it smooths out?) Any other thoughts.


Also, as stated before, cranking the car is very easy. It always starts in less than a second no matter how cold it is.... just with horrrrrrrible vibration.

Thanks!

If you loosen the injector line to one cylinder at a time that will shut off a cylinder. If you loosen the line and there is no change, that is the problem cyl.

Valve adjustment would have to be wildly off to get a miss fire and it would never get getter.