rough running and stuttering.

hi everyone,
I have an e46 318 {03} that has thrown up a few codes and as a result it has been fitted with new o2 sensors and a new MAF sensor, the problem has improved but is still there, the only code im now suffering is P1168 FRP Sensor In Range But Low. I can erase the code but it does little to improve the issue as im not actually curing the problem! My question is, has anyone else had the same issues? and would a new fuel filter put me outta my misery!? thanks Phil.

ok, update..fitted the new filter, worked great, til the next morning, the same problem keeps coming up so i took it to a nearby independant specialist, he diagnosed a blocked/failed cat and fitted another { £325} great, til the next morning!!
running out of ideas and would appreciate any advice before i go the the stealership for some dynamic tests at god only knows what price. all I can think thats left to play with are two cam sensors, 1 crank sensor, fuel pump relay or fuel pump.. and this all started 1 day after i replaced the oil, the filters and plugs!! arghhhhhh.
Thanks for reading my rant and feel free to make constructive suggestions.

ok, this morning i decided to have another play with the car from hell... having spent a fortnight putting off going to the main dealer I decided to remove and clean up both crakshaft sensors, just because they were there and I had'nt! having done it I took her out for a spin and same old same old..rough and sluggish. enough, time for an Italian tune up! I put the pedal down and it struggled..wheezed and objected so much that I almost relented..no I kept on pressing and hey presto!! it gave a great big shudder, cough and sneezed then all was calm..normal running was restored! ive put 200 miles on over the last 24hrs and mostly with a smile on my face:]

So my conclusion is that the cat was blocked as my independant suggested all the crap had backed up inside and made the bank 1 sensor 1 and 2 lamdas sooty and this started tricking the car into over and under fueling, in short everything was doing its job but it all took time to clear through and give accurate readings after the replacement cat was fitted. obviously my actions were based on pure frustration and i wouldnt recommend them to anyone, the point is everything is logical and needs thinking through, i coulda thrown more money at the car but it would have been wasted, think it all through and cross reference everything in these and other forums... the answers are out there!