Hard starting when warm
 

'88 300 CE. Car starts great when cold. When starting when warm, car starts then dies, like its flooded. Then will start the second try. It also idles rough. I just replaced a split vacumn hose. One person thought it could be the temperature sensor. Any thoughts?

The warm restart stall is the nature of the beast. Get in the habit of poking the throttle just when it fires on a hot or warm restart, and it won't stall.

A bit of uneven idle roughness when the engilne is above 60C is also the nature of the beast because of the lean idle mixture. You might notice that it idles smoother below about 60C, which is the about the point where the engine goes into closed loop operation and maintains a stoichiometric (14.7:1) mixture under all operating conditions except WOT. Non-emission control engines idle at about 12.5:1, which is the point of best idle quality.

The Mercedes service literature states that lambda equipped M103s will not idle as smooth as non-lambda versions.

Duke

Hi Duke

I had the same problem with my 102 engine. I know you firmly believe that its the nature of the beast to start and die when hot but I just want to share my experience on this one.

I, for one, do not accept that its the nature of the beast as I have seen no other make of cars do this nor do other MBs do this. My car when I got it 6 months ago would, when warm, fire and die immediately too. Adjusting the idle speed and the EHA did not help (but it did give more power). I used one dose of STP concentrate and after that, a fuel filter change. The problem went away.

My thoughts are that maybe another way to look at this is the car is firing up prematurely from leaking injectors and vaporised mixture on the cylinders and not from the FI system kicking in yet. Try holding the cranking time a little longer and use the injector cleaner.

Regards
Oreo

Hard Warm Start
 

John

You have exactly described the symptoms common to many of us.

Many comments are available if you search.

I have found that you can improve the running of the engine via adjusting the EHA (do a search) and by good maintenance and tune but not solve the warm start & die & start.

The owners manual almost tells you to use throttle when starting a warm engine which I find interesting. That is for a new car.

I have tried Injector Cleaner but strongly suspect the injectors are leaking down after shut-off especially as the engine actually gets hotter before cooling.

So other than getting used to using a bit of throttle when warm changing injectors is the only thing left unknown for me.

They can be done DIY and are not too expensive on the M103. Best to know everything else is as it should be first.

Duke - that was a great explanation on the idling.

Oreo - as far as I know you cannot adjust the idle speed on the M103.

89 300CE
152k kms

Big Blue

My 102 without Lambda has a idle control valve with a bypass screw that allows for idle speed adjust. But when engaged in gear the computer takes over. With idle adjusted to high (900-1000rpm) the engine will start hot and run with dying on the first try, but barely. But, like I said, it was not the solution for me.

Regards
Oreo