Rough idle after Diesel Purge
 

A couple of weeks ago I did a diesel purge on my new to me champagne TD and during the purge the idle kept getting more and more rough. The purge started turning dark almost immediately. Now it shakes pretty good at idle.

Today I did a diesel purge on my new to me black TD. As the purge went on the idle got more and more rough but on this car the purge color didn’t change much.

Both of these TDs need some sorting and cleaning the fuel system was on my list.

Any ideas? I’m thinking something dislodged and is clogging an injector. Checking and/or rebuilding the injectors was next on my list.

Could be some of the dislodged crap clogging the delivery valves or making the injector pintles "stick" a bit. Give it 200-500 miles after the "purge" before tearing into anything else. If it's just dislodged crap causing problems, the injectors and DV's should sort themselves out in a couple hundred miles.

If you can take it for a ride out on the Freeway as fast as you feel you can get away with and like 1 hour long.

I was thinking that too. A good old fashioned German tune-up. I just wanted to make sure I wouldn’t hurt anything by doing some hard/fast driving.

I purged my coupe when I got it a couple years ago and had mild but good results so this result wasn’t expected.

Actually your Engine/Car could be running perfectly and there is no way to predict if some had fast driving would hurt anything.

Did you change the filters after doing the purge?
Did you replace the fuel hoses that you disconnected to do the diesel purge?
You may have air incursion, clogged filters, or crud in the IP
Any of the above can cause a rough idle.

Yep, new hoses and filters

I would just drive it for awhile first. It will do no damage I can think of.

Did a caliper change not long ago and bled the brakes. The pedal remained lower than I like. Certainly far lower than before I changed the caliper out. It still had good brakes.

Not a Mercedes and the brother in law told me to drive it and the pedal will come back. Truthfully I had my doubts . Especially when he said it might take weeks sometimes.

Well about three weeks of daily driving and the pedal was back up. Where the air was trapped and how it got out is beyond my understanding. Even if it was air. Yet it pretty well had to be but the pedal was not really soft. Just low. It is hard to be certain but the pedal returned suddenly I thought over a gradual improvement. With no detectable change in braking quality.

He works on cars continuously. All brands so I respect his opinions. I did go look up the cars brake issues on the web and this model has presented many problems of what are odd issues to me with their brake system. For far too many people. Many got no pedal and had to have the car flat bedded to a dealer. I had exactly that at first with the initial bleeds.

The possibility exists some air got into your hard injector lines and may take some time to clear. In your situation.

The shaking is very touchy. Sometimes it can be due to the engine not firing uniformly, but more often it is due to the motor mounts and rpm. When the rpm hits a natural vibration frequency, the shaking engine can shake the whole cabin. In my 1984, after I changed the motor mounts to better ones, the engine was much better behaved. Now, as I drive it around a parking lot it doesn't shake noticeably at any speed. I recall those were Febi, Made in Germany, but would have to check the log book (out of town). In my 1985, it has been bothering me when cold and just off idle, so I changed the motor mounts this morning to Lemforder, Made in Turkey, but didn't notice improvement. They had the rubbed off rubber labelling and blue dots that people say are "same as M-B brand". But, I was surprised that the old ones were one of the same (almost same height as new) and one that said "Made in W. Germany" (sagged ~3/8"). I am guessing the "West" means manufactured before the wall came down.

As one other data point, I once tried hydraulic mounts for a Corvette, which weren't easy to fit (recut thread & had to jack engine way up to work in). The shaking with those was so unbearable I didn't even drive the car. But, not sure they weren't actually solid rubber since Made in India and <$20. People say that the two "engine shocks" don't do much when the engine is running and are mainly to dampen the shutdown shakes.

Both wagons have new, highest quality motor mounts.

The black TD isn’t shaking much anymore. I’ve only driven it around the neighborhood a few times. It’s not freeway ready yet. I just had the whole front end rebuilt and it needs aligning, new powder coated rims and replace the undersized, 9 year old tires. Then she’ll be ready to fly.

Given that both are new to you, is there any documentation of recent injectors? If none, then I would immediately pull / test / rebuild or replace the injectors.


If the problem remains, you can rebuild the delivery valves.


Interim diagnosis: loosen hard injector lines one at a time, see which line has the least effect on the rough idle, and that is your bad cylinder (either injector or delivery valve).

If an injector is streaming fuel, it can burn up the prechamber and hole the piston, turning your engine into a door stop. Don't let this problem go on and on, you need to address it.

Have the valves been adjusted within the last 15k miles? Get that addressed as well, don't burn up a valve.

I adjusted the valves on both TDs, twice just to double check. No history came with either vehicle. I was planning on doing the injectors because they probably weren't done in the past. I just need to gather the tools and parts.

Send your injectors to forum member Greazzer he has done several sets for me. Great service.

He did the injectors for my coupe. I was going to buy the Monark nozzles from the guy on eBay.