Car Starts Much Better After Sitting a Longer Time
 

This puzzles me. Used daily, the motor cranks for a couple of seconds before starting. Both hot and cold starts; not noticeably different between cold and hot starts. But if the car hasn't been started for several days, say 3 or more, it fires up instantly, like it did when new. Otherwise, the motor runs fine. The injectors are original. New plugs. Regular maintenance. Not great fuel mileage. Car is my W124 with M103 motor (200K on the clock).

What scenarios are consistent with these symptoms? Starts instantly after prolonged sitting, but cranks much longer when driven daily.

Cal, could it be some sort of vapor lock when you start the engine on a daily basis due to the hot/warm ambient temperature?

i have found that situation to be caused by faulty check valve on fuel pump or faulty accumulator at the fuel pump assembly.

Long crank hot starts are caused by leaking injectors. Pretty much all injectors dating to the 1980s should have been recently replaced or need to be.

Thanks for the thoughts all. My indy shares David's opinion about the accumulator, and I lean toward Kent's injector theory. I have trouble picturing the logic of the accumulator/check valve solution, since the longer the car sits idle and the more time that passes for the fuel system to depressurize, the easier the motor starts. Seems totally counterintuitive.

But I'm also not totally persuaded about leaking injectors either, because there is no noticeable difference between hot and cold starts when the car is driven daily. Both require longer cranking than when the motor hasn't been started for several days. As Kent says, hot starts should be harder than cold starts with leaking injectors, and I'm not really experiencing that.

Would fuel pressure/volume test be the proper diagnostic test for both accumulator and injectors, or is it something else?

Cal,
I would think that injector bleed-off is more likely! Could also be a very slight head gasket issue.

The accumulator is MORE for warm to hot re-starts than cold starts.

The cold start valve circuit does not energize until the engine has cooled sufficiently. IIRC the threshold temperature is somewhere in the low 70 degrees F. In warm weather the engine may not cool down overnight to the threshold temperature. My 91 300TE behaved the same way as yours and always started faster in cold weather than warm. Mark