Engine (hot) stalls while idling

Hello everybody, here I am again.

After finally finding and installing a correct Bosch gasoline pressure regulator, I tested my W116 280SE D-Jetronic and unfortunately the problem remains: it does not hold idle when the engine is hot. When it comes on when cold, the engine runs just fine and doesn't stall at all.
Yesterday I drove 4km to get to the gas station..everything seemed ok. Then when I left again, I immediately noticed that the engine would stall at idle speed...and the ride home was unpleasant. Based on your experience...what do you recommend I check? Could a temperature sensor or the AAV be to blame? The fuel pressure is correct..2.0bar. Thank you all. I repeat...as soon as it is started and for quite some time, the engine runs idle fine..at the correct RPMs...the problem arises when the engine warms up.

Thanks and best regards
Claudio
P.S. if you prefer to answer in German that's fine too

Hello Claudio,
does the fuel pressure remain at 2 - 2.1 bar when the motor is warm?
br Hans-Juergen

Hi Claudio,

that is a hard one. An effect that comes only after some time of hot engine sounds like an electrical problem. Mechanical issues would happen earlier. It is most likely not ignition as your car continues ti run. But it would be good to know whether ignition timing fits.

It can be a failing fuel pump or dirt in tank. Hans-Jürgens tip to check fuel pressure while driving is goof. Mount your pressure gauge on windshield.

Or it is D-Jetronic itself. Start with verifying pin 19 (Multimeter to +12V). Must be ground when fuel pump shall run. And then trigger contacts and last signals to injectors.

I would like to point out that if I turn the key just after the engine has stopped warm...the engine starts right away and stays running if I don't go below a certain RPM.
Unfortunately, on my dashboard there is a clock instead of a tachometer and I don't know exactly what RPM number it goes off under.

Hi Claudio,

have you ever measured idle exhaust gas? That could be totally wrong.

And maybe I misunderstood. Engine runs cold and warm well. Suddenly you have a switching point where it stalls if you do not increase rpm. Is that your phenomenon?

Hi Volker, 

let me explain the situation. When I start the engine (cold) it starts right away and it sounds fabulous and runs great. When I do a few miles the problem starts to present itself, and that is under a certain number of revs..the engine simply shuts down. If I turn the key the engine starts right away..but to keep it running I still have to keep the throttle open. In my opinion it is something related to the temperature of the coolant..because otherwise you can't explain that when cold the engine runs great and hot it doesn't. I know your experience is very important...I take advice....

Regards
Claudio

Okay Claudio,

so you do not have sudden change but warm engine runs badly. You can only keep it running at medium rpm.

A cold engine runs normally better than a bad running warm engine. It has more fule and higher rpm due to AAV being open. When it gets warm these effects cease and now it should run all by itself. If that mixture does not fit then you have the effect as described.

You should start with ignition timing. Check it at idle, 1500 and 3000 rpm and check vacuum retard according to MB workshop manual. Fuel pressure was checked by you I know. Then please measure manifold vacuum by inserting a T-piece in hose to MAP sensor for a vacuum gauge.

Did you already adjust idle exhaust gas? Where is CO and HC ?

Hi everybody, 
Yesterday I installed a new ignition coil(right Bosch code). I started the engine and waited for the engine temperature to reach 80 degrees..the engine did not turn off by itself. After that I went on a small country road for a little ride...feeling that the rpm were low in idle mode..I turned two turns of the air passage screw...the rpm went up to the right point.
Basically I think I have solved the problem..although I want to bring everything back to the original so soon together with a mechanic I will mount the original injectors and rebuild the fuel line as per the Mercedes diagram.
I still have to study my old Bosch manuals (they are in German so I have to translate them all) to be able to perform all those maintenance tasks that the great Volker listed on this site.
 
Thank you all.
Claudio

Hello Claudio,
then you can on 10.09. have a nice birthday trip with your Mercedes
BR Hans-Jürgen