Joel, How cold has it been around there lately? The cold start valve is located between the number 3 and 4 intake runners. It looks like an injector (which it is basically). Held into it's own cute little manifold by 2 screws. You've got to remove aircleaner assy to get a look at it. It sits between the head and the injector fuel distribution block (big aluminum octopus with fuel lines coming out to each injector). There is no maintainance schedule for that part that I am aware of. When it doesn't work, you replace it. You might wonder what it does. Simply under certain conditions, ie cold start, the ECU sends an email to the cold start valve telling it to squirt a little fuel into the intake air flow to richen up the mix to get an easier start. How do you know it isn't working?? Well hard starting in cold weather is one symptom. Another could be if the valve hangs open and tries to flood your engine. (not likey, but possible). How to check it?? There are fancy ways and back yard mech ways, but the safest is to get it checked by a mech who knows about fuel injection systems. The quick and dirty way is to remove the 2 screws, gently lift the valve out of it's seat, have someone crank the engine and visually inspect the output of the injector. WARNING, I DO NOT RECOMMEND DOING IT THIS WAY, AS THE POSSIBILITY FOR A FIRE IS HIGHLY LIKELY. YOU HAVE BEEN WARNED. After sitting for 5 days, it's more likely that your fuel system has bled down and needs to be repressurized by cranking the engine. If it starts(you didn't describe the starting problem other than difficulty), shut it off immediately. If it starts right up on the second try, the it's probably not the cold start valve, but system pressure bleed down. I hope this helps

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Jeff L
1987 300e
1989 300e
1987 BMW 325