Hi everyone, its been a while since I posted. But I have been doing a lot of reading about my recent MB projects I started in December 2023.
I recently acquired two 560SEL (1987 and 1988). Both in decent condition but different issues. Currently I'm working on the 1987 and I ran into an issue I could not solve so far by studying the forum or you tube.
The car fires up great and idles a bit irregular but good at around 700-800rpm. Then after a minute or two it gets rough, almost like running on only some cylinders or so until it eventually stalls.
Here is what I did so far just to give an idea of things already done (not necessary related to this issue as it wasn't there when i acquired the car).

- did the timing chain replacement incl. rails, injector seals and holders and the big vacuum lines connecting to them. Dropped oil pan to check if clean.
- replaced all belts
- did a coolant flush to replace coolant with what's considered the correct coolant.
- replaced all rubber fuel lines from tank to pump and return to tank plus accumulator as I had a warm start issue.
- then I replaced manifold gaskets as I had an exhaust leak
- then the car wont start at all (just cranking), replaced the ignition coil and it starts right away.(but still stall when getting warm)
- ohm tested the crank position sensor => reads good.
- disconnected the idle air valve to see if this makes a difference to my issue: just higher idle after startup, but will still show the issue once warm

I was considering a fuel supply issue, but pumps running fine and the following makes me believe its an air related issue:
When the car starts getting into rough idle and I gently push the air flow plate with my finger down (air filter housing of course removed) and with just a tiny little push the idle will recover to normal.
On Benzworld a similar issue was described but only with assumptions, no solution (https://www.benzworld.org/threads/56...g-why.2834985/).
What could be the potential reasons according to you guys experience? I think may be vacuum leak, but before I jump into a smoke test, maybe someone has a simpler idea about a fix or something to try?
Thank you for your comments!

 

Update: I got a reply on BenzWorld and the issue was the O2 sensor.

 

O2 sensor and vacuum leaks both common.

Even with a fresh O2 sensor it is good practice to check for vacuum leaks.

 

I did order a new O2 sensor and some tools related to the job.
I also have a smoke generator which i will use in the next few days. Thank you for your input!