Revs not increasing past 2000 rpm.

[Viv Rees]

Help, any ideas welcome. My old tuscon, year 2006, 1.9 crdi sometimes fails to rev past 2000 rpm. Fault can be erased via Obd reader, but comes back, fault reads as mass air floe sensor, I have replaced twice, I have also changed EGR valve as existing was totally clogged. When I changed EGR valve I noticed there was oil in the base housing for the valve, car ran ok but then same fault again. Is is it normal to have an amount of oil in the base housing of the EGR valve? and is there something else that I should be thinking of, diff sensor perhaps?. Thanks in advance, cheers Viv