My C320 2004 model is very slow to accelerate. I have to pedal down completely to move.I have serviced it, changed transmission fluid and filter and also changed fuel filter and air cleaner, please some one help me.

Pull codes. This is the equivalent of asking the car where it hurts. Anything that makes a C320 240D slow or worse will almost surely trigger a code.

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It could be something as simple as the throttle cable being out of adjustment. Sitting in park if you press the pedal does the engine rpms rise right when you begin pressing it?

M112 engine is drive by wire and uses a cable from the pedal to a throttle position sensor on the drivers side under the hood near the firewall.

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Plus two on checking codes. You don't say where you're located, but if you're not in CA you can go by autozone (and some other parts stores) and they will check codes for free. Guessing at things and trying different solutions (as it sounds you've done) is just frustrating, time consuming and expensive.

Of course I typically recommend that everyone who's interested in their car should have a basic code scanner, the MS309 is a nice basic standalone OBD-II compliant tool and is about $20 on Amazon.

If it is the Throttle Position Sensor it's relatively inexpensive and easy to change.

In the meanwhile I'd certainly try the adaptive throttle/shift reset procedure (unique to the five-speed transmission), it's easy and free and it won't do any harm.

Good luck.