Clattery when cold
Join Date: Feb 2012
Location: United Kingdom
County: Greater London
It's really hard to check with finger pressure as the vacuum actuator acts as a strong spring that masks how free the VGT mechanism is or isn't. The only reliable way to check the VGT vanes aren't sticking is to test with a Mityvac (or cheap Chinese clone - ~15GBP on eBay) vacuum pump, connected to the actuator with a bit of hose. The actuator should move proportionately right back to the stop as you increase vacuum from 0-approx 18cm Hg (full range of the actuator is specced at 0-20cm Hg). This is about 2cm total movement at the lever end, not 1cm as eLearn states. If it jams and stops part way, or the movement isn't linear, the variable vane is sticking due to carbon and/or rust. Aerosol cleaners can deal with carbon, but not rust. It often is rust, just a tiny bit on the cast iron surface jams the moving vanes. Or, more rarely, at very high mileages you lose movement in wear to the VGT mechanism itself, within the turbo.
I think it's worth taking the turbo off and doing the job properly. It's then just 4 bolts to get inside the exhaust side of the turbo and clean it up and check for wear. It's also a good opportunity to check the general condition of the turbo impellers, seals and bearings. You have to detach the front cat from the turbo to use an aerosol and that is the hardest bit of removal anyway, thanks to the ferocious V-band clamp. If rust is the cause, you won't find out until you find it still sticks, so have to do it all again.
EDIT: and the vacuum used is created by the vacuum pump on the gearbox end of the cylinder head - the round, silver can thing, it's driven by exhaust cam rotation. It seldom goes wrong. What does very commonly go wrong is the vacuum pipe between the vacuum solenoid and the turbo vacuum actuator splits or develops tiny holes, that leads to lack of or erratic boost at low revs. Definitely the first thing to check, and it's a cheap and easy fix to replace (3mm ID silicone tube).
Last edited by halftone; 30-03-16 at 10:54.