megane scenic 1.9dci mk1 Fault 1815 no power

On my 1.9dci mk1 scenic I have lost power going up hills and on the flat I cant get over 70mph. and when in gear she will not go over 3000rpm but when not in gear from start up revs perfect.
I have replaced both the MAF and the EGR. My local garage has plugged in and the fault reads 1815 Inlet Air/ Boost pressure circuit but hes not sure what these means can anybody please help. we are guessing it my be air filter, air leak somewere or a sensor. I only just managed to get in the door before he closed but he kindly said if I can narrow it down it might be able to squeeze some time in the morning please can someone advise as im suppose to be taking my daughter to her first concert tomorrow nite

	MAF MAF A mass airflow sensor is used to determine the mass of air entering the engine. The air mass information is necessary to calculate and deliver the correct fuel mass to the engine. Air is a gas, and its density changes as it expands and contracts with temperature and pressure. In automotive applications, air density varies with the vehicle's operating environment, and is an ideal application for a mass sensor. (See stoichiometric, ideal gas law, and density.) There are two common types of mass airflow sensors in usage on gasoline engines. They are the vane meter and the hot wire. Neither design employs technology that measures air mass directly. However, with an additional sensor or two, the engine's air mass flow rate can be accurately determined. Both approaches are used almost exclusively on gasoline burning, EFI (electronic fuel injection) engines. Both sensor designs output a 0 - 5.0 volt signal that is proportional to the air mass flow rate, and both sensors have an IAT sensor (intake air temperature) incorporated into their housings. When a MAF is used in conjunction with an exhaust gas oxygen sensor, the engine's air/fuel ratio can be controlled very accurately. The MAF sensor provides the open-loop predicted air flow information (the measured air flow) to the engine's ECU, and the EGO sensor provides closed-loop feedback in order to make minor corrections to the predicted air mass.

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megane scenic 1.9dci mk1 Fault 1815 no power