I have a 1983 240D with 230,000 miles on it. In August it started to run rough when you stopped at a red light BUT it idles kind of "ok" when its cold. Not perfect, but not shaking the car as hard as it does hot. I have changed the air cleaner, both fuel filters, ran a purge, changed the glow plugs with Bosch glow plugs, changed the injectors and the seal ring under it. (heat shield?) It runs great at speed. The other thing I have noticed is a slight lag when you turn the key off or paranoia. I have just returned from a 500 mile trip so I trust the car, its just the cold hard starting misfiring until it warms up some then it seems to idle "ok". Stumble a little when you first go, then stop at the red light 32 miles later and its stumbling and running so rough that the car shakes and you are afraid it will stall. Engine temp is in the same range so I have ruled out a compression leak and not losing coolant. Timing chain stretch?
Any ideas, besides a complete overhaul? I have a spare injector pump if it comes down to that but I really don't want to get that drastic. Also how can I ge to the filter/strainer in the fuel tank without dropping the tank? Is there an access through someplace like in an Audi?
Rather find a cause and cure.
Thanks!
drujinin

 

Check for a leak at the fuel pump inlet. The pump may be sucking air past the primer or a loose/rotted hose. Also, when was the last time you replaced motor mounts? If it's more than a5 years then it's probably been too long. Engine shaking is worse with bad mounts. The fuel strainer is in the tank bottom, a 46 mm socket is needed.A 46 also removes the sending unit from the top of the tank too. It's easier to do a visual from the top with the fuel drained.

 

I would have to agree about checking the motor mounts and the fuel line. I had a similar problem a while back. Rough idling after cold start. After mucho dinero to the dealers shop to change the mounts, tear down the fuel pump and new manual fuel pump, it still had the problem. I went in to pick it up when they said it fixed, started it, and the problem was still there. As we were looking at the engine while it was chugging away, I pointed out that there seemed to be air foaming in the pre-filter. Was this normal? It would disappear after this car warmed up. The hose before the pre-filter was old and cracking. When they replaced it the problem was gone. That cheap fix cost me over $900. Do the visuals for the obvious. I'll bet you need new motor mounts also.

 

For the lag at key off. Has the vacuum pull off in the back of the injector pump been changed? If so the spacing gaskets were not installed properly. What happeningat key off, is thatvacuum is applied to thediaphragm in the pull offat the rear of the pump. It pulls the injector rack to close and the fuel flow stops. If the pull off has not been changed and it is not leaking (sometimes they fill with oil due to a failed diaphragm) then the engine is weak on vacuum, or has a vacuum leak. Most probable leaks are the the hoses under the hood from the brake booster to the vacuum spliters, the door lock diaphragms and the driver door lock switch. Have you seen any problems with weak vacuum and low oil level in the engine? If so the vacuum pump reed valves or valve seals are leaking. Test this by keeping oil level near the top of full and see if it helps. When oil level is a quart low does it make a difference? One thing, never, ever, over fill the crank case. This causes excessive crank case pressure in some cars and leads to blown pan gaskets and crank case seals.Thought you should know in case you were planning on testing the reed valves by overfilling the oil level.

 

OK! Thanks! For some reason after reading through here and seeing the comments about leaky fuel lines. I ended up replacing 6 feet of line in the suction and 4 feet in the return line. They were rotted out right in front of the rear wheel. UNFORTUNATELY it didn't help the cold starting or rough idling.
Right now I have adjusted the valves and checked the voltage on the glowplugs before starting. I feel the glow plugs shouldn't be the starting problem.
As soon as you start cranking, the engine starts firing but it seems to be balky. Then it peters out which I think are the glow plugs getting cold. Stop and reheat them, then start cranking again, the whole time its firing and cranking faster and faster until its almost running at which point you have to keep the starter engaged and overspeed as you press the foot feed to get the engine to take off and run. Right now it hasn't been below 30 degrees and last year it started all the way down to 10 degrees without a block heater.
I am going to look into the motor mounts issue this weekend. Can I get them aftermarket? I would hate to have to buy them from MB.
Thanks!

 

Have you pulled the prefilter and inspected it and also make sure the primer valve is not leaking? On an 81 300D the prefilter looked clean with only a small amount of dead algae on the inside. The engine would not make power above 55 mph. Thought the pump was shot and there had to be a leak at the pump. Finally pulled the filter and saw it was completly plugged with dead algae. The design of the prefilter prevents you from actually seeing if the filter is blocked. New filter and problem was solved. Let us know if there are any leaks, anywhere; secondary filter, injectors.

 

Motor mounts. Aftermarket's are about 20 dollars and are good products To keep them alive don't let fuel or oil leak onto them. If it does wash is off ASAP with soap/water.

 

Have you tried to adjust the rack damper bolt? There's an upgrade bolt available also.

If you are going to change your motor mounts, check your oil cooler lines to see if they need replacing. They're good jobs to do together.