I've got a serious cold start issue. When the weather is warm 70F+ at night, this is not an issue, but once the temp at night drops below 70, then this starts to happen and it's worse as the temp drops lower. When I get the in the car in the morning or after it's sat for a good while (like at work for 8 or 9 hours and the sun goes down), it takes forever to start the car, it just turns over and turns over and turns over, then it chokes a little bit and won't start but feels like it's starting to catch and finally after literally 5 to 10, sometimes 15 minutes of cranking the starter, it starts up. When I step on the gas it feels like it's going to stall and sometimes when I'm at a light it will feel like it's going to stall as well, but if I shift into neutral it seems ok.

I've checked the OBD and there are no warning lights, I've replaced the coolant temp sensor/switch. I've replaced the spark plug wires and distributor cap, all of which helped a minuscule amount, but, nothing has fixed the problem. I've noticed that when I run Shell Premium (93) it seems to be better than other brands like Hess or off-brand. Also, if I dump a bottle of octance booster in there, it seems to dramatically help the problem, but it still doesn't go away.

Any thoughts? Oh, and there's a big difference if I have it in the garage (unheated) or just sitting outside overnight. If I let it sit outside overnight, I'll literally run the battery dead trying to start the car.

Thanks for any help suggestions or thoughts ('92 300E, approx 210K mi)

 

I believe you are looking in the wrong direction for your problem. Ones you pressurize your fuel system, you are fine untill long break and loosing fuel back to tank through return line. First check if your fuel pump relay and pump go on with ignition key every time you turn it to position 2. I would turn the key on and off few times before actual cranking to make sure the fuel rail will get enough pressure. It should start a lot sooner. Then take off fuel supply line by the engine, insert it to a container and turn your key on to see how much gas will the pump deliver in 30 seconds (should be no less then one quart/liter). This test will show if the pump and fuel filter are still good. If there is a fuel pressure port on your rail, usually 50 to 55psi should be seen on pressure gauge by injectors. I believe that bad fuel pump or just the relay could be your problem.
Bernard