Engine dwindles at 2500 turns

hello have the following problem on my carisma gdi build year 1998 with 125 ps and that is I just can not get out over the 2500 turns and if only if I give gas very slowly. I have now: changed the timing belt because the old was not properly aligned new air quantity meter new lamba sonde new kat also let the error code read out but there was nothing in it. I don’t know now what it can be anymore would be nice if you would help me salute martin