i have a:

1998 Mercedes C240 Elegance, 2.4 V6, 110k mileage,

When i turn the ignition the car starts and revs slightly like any other car, then just drops the revs and turns of, does not hold the revs at the idle speed of 800rpm like it used to unless you physically press the accelerator.

The mass air sensor and spark plugs have been replaced along with a thorough cleaning of the exhaust system.

This is really baffling me, any ideas or thoughts from anyone would be very appreciated.

i would check and see if the mass air flow sensor is pluged in good and the wires going to it are ok allso check and see if you have any craks or holes in the intake