300sd rough idle when hot

[Ncbenz]

So I've been tackling all the problems on my 85 300sd and the last thing I need to solve is the rough idle. I've done everything I can think of.

Head gasket
Timing chain
Motor mounts
Tranny mount
All fuel filter and in tank scree
Air filter
Balanced injectors (1950-2000psi)
New lift pump
Valve adjustment (5k miles ago)
New rack damper bolt
Compression checked out within spec and balanced

The injector balance mad the biggest difference. After I did it the idle is perfect when cold but after i get it nice and warm,like a highway drive, the idle will be rough and shaky.

What should I test next? I heard it could be the delivery valves but they seem impossible to track down.

[tdoublenastywitit]

A good rule of thumb when idle is worse when warm is to look at injectors

Edit: sorry didn't see u balanced the injectors

D. Valves cost like $20 to replace u get them at any Bosch service center or dealership

[Father Of Giants]

$20 a piece right?

I'll try replacing the valves one day.

[Ncbenz]

20 bucks? Is there anyway you can send me a link to get them?

[tdoublenastywitit]

Delivery valve seals $20 bucks total. Maybe I'm exaggerating a little it's more around $30.

It's really hard to get them online u gotta just goto any machanic shop that has the "Bosch Service Center" banner at it or the Mercedes Dealership and they order them there. It's not something they will usually have in stock but they will get it to u within a week or so.


Go read the "delivery valves of a source of knocking" thread. (Huge thread should be a first or second page) Just skim thru the first thru pages I believe a few members post the part numbers which u will need.

[Diseasel300]

More like $30 for EACH PIECE. You're talking ~$300 for new D/V's. That's halfway to a rebuilt and calibrated IP. If the DV's are that worn, imagine what the rest of the pumping elements are like?

The OP can try polishing the DV faces, but failing that, it would be wise to find a good used IP or have the one he has rebuilt.

Before getting too carried away, check for air ingress in the fuel system, health of the lift pump, and fuel pump supply pressure.

[tdoublenastywitit]

Originally Posted by Diseasel300

More like $30 for EACH PIECE. You're talking ~$300 for new D/V's. That's halfway to a rebuilt and calibrated IP. If the DV's are that worn, imagine what the rest of the pumping elements are like?

The OP can try polishing the DV faces, but failing that, it would be wise to find a good used IP or have the one he has rebuilt.

Before getting too carried away, check for air ingress in the fuel system, health of the lift pump, and fuel pump supply pressure.

Ok then I'm very confused then.... Hahaha don't mind me.

[Ncbenz]

The lift pump is brand new so I now that's good. I did see this morning that there are small air bubbles in the clear line leaving the IP. There is no air entering the ip through the clear hoses. Could the ip be sucking in air? If so from where?

[Alec300SD]

Originally Posted by Ncbenz

The lift pump is brand new so I now that's good. I did see this morning that there are small air bubbles in the clear line leaving the IP. There is no air entering the ip through the clear hoses. Could the ip be sucking in air? If so from where?

Copper crush washer on the pressure relief valve.
The aluminum crush washers on the banjo bolt for the clear hard fuel feed line at the IP (or the clear hard return line).
A crack in a clear hard feed or return line (typically by the barbed fitting).

[Ncbenz]

Any ideas?