right I went to view a 2000 plate octavia tonight was told it wasn't boosting... fired it up and it seemed to run OK but as previously said its not boosting

after further investigation I heard the n75 valve clicking.. I could also feel it doing this when I put my hand on it. so is this a sure sign its goosed or could there be more to it?. all in I've got the chance of it mega cheap so should I go for it?

its done 128k

stamped service book to 110k

the last 25k has been mainly door to door being used by a window cleaner

It does sound like the n75 valve is broken, but you need to check that there is travel on the actuator on the turbo when a vacuum is applied to the pipe too.

What engine is in this 2000 TDI? I think some are vacuum related and others positive pressure (don't quote me on that). But still either way, if one was under the car you should be able to manually move the actuator arm smoothly (assuming the vacuum pipe at the n75 end is temporarily disconnected). 25k or short stop/start miles.... the turbo may well be seized up to some degree (hence needing to check if the control rings are jammed up)

I trust the cambelt has been changed (twice?), 60k/4 years intervals.

It does sound like the n75 valve is broken, but you need to check that there is travel on the actuator on the turbo when a vacuum is applied to the pipe too.

What engine is in this 2000 TDI? I think some are vacuum related and others positive pressure (don't quote me on that). But still either way, if one was under the car you should be able to manually move the actuator arm smoothly (assuming the vacuum pipe at the n75 end is temporarily disconnected). 25k or short stop/start miles.... the turbo may well be seized up to some degree (hence needing to check if the control rings are jammed up)

I trust the cambelt has been changed (twice?), 60k/4 years intervals.

yea just picked it up. timing belt has been done twice. I disconnected the MAF and its boosting so looks like ill be heading down that direction

Get vagcom on it and see what fault codes are logged before you start shelling out for bits..... my is my theory and then replace the cheaper bits first.

The CTS can cause strange issues too. Is yours a 90 or 110 (think it is too old to be a 130)?

its the 90bhp sadly

oooh.... a 90, the later ones had VNT based turbos, the earlier ones didn't, and as yours is probably pre-face lift I would hazard a guess it wasn't VNT, and thus the n75 controls the wastegate on the turbo (I think that is how it works.....)

replacement MAF fitted and connected and the car is running on full power so all is looking good.