I’ll try cracking the lines and see what happens. With worn compression doesn’t it surprise you it would go so easily on a first crank and fire up INSTANTLY? I mean I don’t doubt that it could be very well be compression, but it’s a little shocking it wasn’t hard to start.

Also I had this same issue with a 92 300D. I don’t remember if the exhaust was puffing or not, but the fuel filters were so nasty and the injectors and injection pump were filled with algae! The car idles exactly like this. https://m.youtube.com/watch?v=qJ6vQRImgOA

__________________
Only diesels in this driveway.
2005 E320 CDI 243k Black/Black
2008 Chevy 3500HD Duramax 340k
2004 Chevy 2500HD Duramax 220k

Really, this is one of those cars that has me really thinking.

Here’s more things I thought of?
What does cracking the injector lines prove?

It has 6 new (just about) glow plugs, but even with that in 30 degrees, if it had low compression wouldn’t the motor be hard to start? It went over the first crank and fired up immediately.

It has 6 new fuel injectors. I also realized I worked on this car not too long ago (local car) and remember driving it when it had about 10000 less miles on it. It definitely did not used to have this rough idle and low power problem.

__________________
Only diesels in this driveway.
2005 E320 CDI 243k Black/Black
2008 Chevy 3500HD Duramax 340k
2004 Chevy 2500HD Duramax 220k

In my first reply, I was referring to a good engine. Crack a line to create a "miss". You'll notice it at idle, but rev the engine and it'll run smooth.


In troubleshooting the engine in question, cracking lines will find you the trouble cylinder.


New parts don't mean anything. If you have a mechanical issue that's developed since they were installed then you have an unrelated issue that needs a fresh eye.


You keep going on about low compression and starting performance. Get over it. You can have 5 healthy cylinders and 1 lousy one. If any of the 5 healthy ones light off, the car will start right up with a crap idle from the missing cylinder.

__________________
Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]

No it doesn’t at all. It points to me they were to trying to fix something. Probably has been an ongoing issue for awhile. I’ll just crack the lines and see what I get. If it points to a problematic cylinder I’ll go from there.

__________________
Only diesels in this driveway.
2005 E320 CDI 243k Black/Black
2008 Chevy 3500HD Duramax 340k
2004 Chevy 2500HD Duramax 220k

It only takes a single cylinder with a compression issue to affect the idle and low RPM smoothness. The "puffing" noise you mention in the exhaust is a clue. If the other cylinders are operating normally, you'd fully expect the engine to start normally, just with that one chugging cylinder. A 4 or 5 cylinder engine would be harder to start with a weak hole, but a 6 will still fire right up if the other cylinders are healthy and the glow plugs work.


Take the time to diagnose. Crack injector lines to isolate the problematic cylinder, then dig in further.

__________________
Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]