Drop of power at 4000rpm with a squeeling noise, help!

[Cupra R Boy]

Can anyone please give me some advise as the Seat garage cant help at all.

Ive had my LCR for 2 and a half years and love it bits but have always had a slight problem which occurs every few month for 1 day at a time. If you put your foot flat to the board at low revs it picks up speed perfect and then a squeeling noise appears at approx 4000rpm and the power drops off for 1 second and then kicks back in, any ideas coz i havn't got a clue and either has the Seat garage?
Now the car has been in the garage for over 1 week as the problem is there now in every gear, every day and they still cant find the problem as nothing shows on the computer as a fault. All i get from them is they say its like sh*t off a stick. Well they should have drove it when it was working
A bit long winded i know but i need help. They even changed the diverter valve as i thought that was the problem but it hasn't worked. Im sooo confused

HELP!!!

 

[ArosaRacer]

mine done that is your TIP to Maf pipe tight as that was the proplem on mine

 

[jonathanp]

maybe too much play in the shaft of the turbo? blades rubbing against the casing or something?

 

[Cupra R Boy]

Im awaiting a call from the garage 2moro as they have arranged to get another LCR in to compare performance. I'll mention both things although they probably wont do anything about it.

If its as simple as tightening a pipe i'll not be happy 2moro. I hope it is that though, cheers lads.....

 

[Madmile]

My turbo sqealed badly with a knackered maf, log the maf with vag-com.

 

[andycupra]

i presume the dv has been checked...

is it mapped?
as the 1sec pause could be due to overboosting?