I'm new to the forum but I may have a serious problem with my 1999 E300D that may end up costing me a lot of money. Several people have suggested you guys could help so here's my story...

I bought a wonderful 1999 E300D with 75K miles on it several months ago. It seemed to run fine when I bought it buy with a hint a miss at idle. I had previously owned a 1984 300D that shook a lot so the 1999 model seemed smooth as silk by my comparison.

It needed glow plugs so i had a shop do that work for me. After I got it back the car had a very noticeable knock that it didn't have before and it ran rough. After my complaint they took the car back in and adjusted the timing. The knock was gone and I drove away. A week later it started missing during idle. Just one cylinder once in a while.

At this point I finished converting the car to VO. (I've been doing VO for years and know what I'm doing in this area.) As the weeks have gone by the miss has grow to become consistent at idle and I'm trying to get it fixed.

Here's what's been done so far:

1.) Air filter replaced
2.) Run 'Diesel-Purge' through engine.
3.) See-Thru filter added to fuel line feeding lift pump. No air seen in fuel.
4.) Cracked injector nozzle lines and found miss isolated to cylinder 3.
5.) Switched nozzles between cylinders 2 and 3. Miss still at 3.
6.) Removed all nozzles. Professionally cleaned & tested. All fine.
7.) Replaced injector nozzles. Problem still at cylinder 3.

Here is the most troubling symptom of all. The miss goes completely away when I first switch to VO. My feeling is this is because the VO is a slightly higher viscosity during the first few minutes as the cool initial VO mixes with the diesel fuel in the injection pump. Anyway, until the VO gets to around 160*F the car runs perfectly. At that point the car misses on VO just as it does on diesel.

Now my mechanic wants to pull the injection pump and rebuild it for $2,500. That's a lot of cash and I'm wondering if there might be something less drastic. It seems to me that the IP is not generating enough pressure on just cylinder 3 during idle. This could be rubbish but is there any way to adjust pressure on 3 without rebuilding the whole thing?

I've read a few things about delivery valve O-rings and delivery valve adjustments but without a picture I can't make any sense of it.

Can anybody help?
Thanks.