this has been a progressive problem over last 3 months. after a few seconds it runs perfectly. if it sets for only a few minutes after running, it starts fine. only if it set for awhile. I've replaced the start injector, engine temperature sensor for the CIS-E controller, idle control valve, MAS controller, fuel pressure regulator, electro-hydaulic actuator and the fuel backflow valve at the pump was replaced three years ago.Could the backflow be bad again? All the vacuum hoses have been replaced.my 90 300sl is just this short of perfection, any ideas?

 

after pondering the problem, i'm almost sure it's an injector leaking off. what's left?

 

Your diagnosis of a leaking injector(s) sound logical to me. I have known other makes of cars to have that problem too. Some people inexpensively treat the symptom by installing an extra switch to control their fuel pump. They shut the fuel pump off a couple of seconds before turning off the ignition, which lowers fuel system pressure. With fuel pressure down, there is not much to push the fuel pass the injector and into the intake. I also own a Weber carburated car which suffers the same symptom as yours when it is very hot outside. If I shut the fuel pump off first before shutting the engine down, then the problem goes away.

 

it was the injectors. starts and runs perfectly. easy job if you don't drop an injector lockscrew behind the starter, so be careful.