I’m cautiously optimistic that the rough idle problem has been solved. I took nhdoc’s advice since this seemed to make the most sense because the problem started after I had the IP seals replaced.

I checked the torque of the delivery valves. I was shocked by how much they were over torqued. Against my better judgment (I don’t always let that stop me) I decided to slightly loosen the delivery valves. I was hesitant because I wasn’t sure that the copper washer would re-seal after being crushed but I figured in a worse case scenario I would replace the seals and o rings again.(but I’d do it myself this time) Well, it took a lot of muscle on a long ratchet handle to break them loose. I re-tightened the seals to 35 NM and put everything back together.

After two days and about 100 miles, the rough idle is gone, regardless of weather the engine in under load or not. I don’t see any fuel seepage around the delivery valves yet. At first I thought the engine was “clacking” a bit louder that it used to, but that has quieted down a bit. I figure I’ll do a diesel purge on it to see if that quiets it any further but I’m so glad to see the rough idle gone.

Now I’m wondering why the wrong torque would effect the idle. Is it that over-torquing causes the plunger to bind somewhat. If this is the case it might explain why it does not idle rough when it’s cold. I’m assuming that when the engine is cold or under load, the EC adjusts the rack position to provide more fuel. This increased flow position can overcome any binding in the plunger, where a “normal” idle position of the rack, cannot.

My other theory is that over tightening puts too much of a pre-load of the delivery valve springs and increases the cracking pressure, which again, cannot be overcome at normal idle fuel pressure.

Either way, I hope this fix lasts. It’s a good feeling when a problem is solved and the car runs as it should. It would have been a lot more difficult to find the cause of this problem with out this board. All the dealers and techs that I have talked to have been of little help. The dealers tried to sell me an IP saying that it had no serviceable parts.

Thanks to all once again.

Nick

W210-025
1998 E300 TD
160k

Hi Nick,

Glad to have been of help...I'm sure you solved the problem. Overtorquing has caused this same condition before. While I am not 100% certain why it does I have heard that the entire IP body can warp ever so slightly causing the plungers to bind. The exact procedure you followed has cured others with the same symptoms but it is always good to have one more case to hang ones hat on. The clacking you hear after cracking open the fuel system is typical and most likely caused by air you introduced into the hard lines that had to work its way out...usually it does in a few miles driving but I have heard sometimes it can take longer...

In the words of Dr. House "everybody lies". That goes double for mechanics. They will swear on a stack of bibles they followed torquing procedures but almost never do. My lug bolts were so tight after I had my tires changed I had to stand on the end of the lug wrench and rock all my 200 lbs to break them free, after they swore they would torque them to the 95 ft-lbs spec. Yeah, right. I figure they were at least 200 ft-lbs.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz

Just wanted to add my solution to this thread on what ended my rough idle...
Same car as Nicks1 here - 1998 E300 TD. Approx 139k on the odo. Symptom: rough idle in park or neutral only after car warms up (hitting roughly 80 on the temp guage) While car was in drive, no problem on idle. And when car was cold (below 80 on the gauge), no problem) - (although it was a bit rough on deceleration around 10 mph also). Anyhow, here's what my journey was to the solution. Rough idle was not fixed until the final repair below..... read on.....
1. Motor mounts were new - just replaced per receipts before I bought the car.
2. I added several doses of diesel kleen to the tank and indulged myself with several italian tune ups.
3. Fuel lines checked for air bubbles several times - nothing
4. Fuel filters, air filter replaced
5. EGR valve checked, not failing
6. Fuel shutoff valve replaced (was leaking)
7. Coolant temp sensor replaced
8. Heat exchanger replaced
9. Probably something else here I'm forgetting. (cocktail impact here)
10. Injector pump - PROBLEM SOLVED

After the new pump was installed, it's smooth on deceleration and idle in neutral or any gear idle is silky smooth also. Just finished a 300 mile road trip and may have exceeded the speed limit by a few mph. You know, 58 or 59.

Hope this is info is helpful. And yes, the cost of the above repairs more or less went from cheapest to most pricey. But I love my E300.

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Barker