Hard start

I have a 1998 CLK320 and for some reason it has difficulty starting after sitting for a few hours. I took it in for repair and the replace the air mass meter and the fuel filter. Unfortunately that didn't work. The car
will start but it crank for about 5 seconds before it finally starts. I'm thinking it may have something to do with the fuel and air mixture but I'm not sure. Has anyone else had this problem? If not are there any suggestions of the cause?
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Loss of rest pressure due to bad check valve!
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Thanks. Is this something I can do or should it be taken to a mechanic?

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Well,not that mechanic that throws parts at it! You can do it yourself and the check valve is near the fuel pump! Also one other common cause is leaking injectors!But 80 to 90% of the time,it is the check valve! Plus check valve is WAY cheaper than airmass meter!
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I had something similar that may help you diagnose your car's problem. I own a '97 E320 (straight six). After about 15K miles I noticed that hot starting was sometimes delayed; cold starts were fine. If the hot engine stood for say an hour or three the start was delayed and the engine started like it was "flooded". On such starts the exhaust reeked of fuel. I checked the fuel pressure regulator but it was OK. By 36K miles I found the problem.
The fuel rail's pressure is about 45 psi.; one fuel injector was leaking fuel into its intake port after shut down. Fuel vapors filled the intake manifold and so over fueled ("flooded") the engine; excess fuel seeped into #6 cylinder and wet its spark plug causing some initial misfiring.
The repair was to replace, in this case, #6 fuel injector - 2 hours labor and about $140 in parts. The engine now starts (hot and cold) perfectly, as it did at the M-B factory in 1996.
I hope this helps you.
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Yes it does. Thanks for the information.

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I agree with TG on this... leaky fuel injector.
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