misfire and knocking noise when revved over 3500rpm

[barnsey406]

hi,my 2nd post here and unfortunately the same problem!
my 406 hdi 110 runs ok,drives ok but the engine sounds slightly knocky?the car drives ok but when i rev the car to 3000rpm or just over the engine shudders,misfires and almost cuts out(this is when stationary)if im driving and take it over this i get loss of power untill the revs come back down again.had the bonnet open and when i rev it and it starts to miss,i notice smoke coming out of the egr valve as if its overfueling?
me and my mechanic freind are stumpped????
changed the injectors,checked the egr valve and also checked the cat and these were all fine.
pls pls somebody help!
many thanks!

[lozz]

Are you sure its not the Egr stuck open,
they can cause the engine to knock /clatter,

smoke coming from the top of it is a sighn something is blocked id guess,
have you tried unlpluging the egr solenoid to see if it improves

[barnsey406]

dont think its the egr valve,had it off and the valve is moving both ways.

[steve_earwig]

Dirty MAF?

[barnsey406]

dirty maf,whats that? sorry if i sound a total twit.......regarding mechanics i am lol!

[steve_earwig]

Mass air flow sensor, it's just after the air filter. Give it a squint but only try to clean it if you can see it's a mess - they break and aren't cheap.