I recently bought a high mileage MK2 Superb 2012 Diesel Estate 2.0 TDI 4x4 AWD II 3T5 1968cc 170HP with 180,000 miles on the clock. The seller was asking £1800 and when I asked why it was so cheap he said there was an engine fault but didn't seem to know what the issue was?  I suspect he thought it was probably going to be an expensive repair? It was!

I paid £1650 and when I got home I used VCDS and found there were no error codes, so they must have been cleared before I bought the car. For the 1st week the car drove well and I was driving it 100 miles a day there were no warning lights on the dash and the car drove well other than a lumpy tick over. After this short honey moon period the little coil symbol and engine management  lights started coming on the dashboard and the engine would go into limp mode, until you stopped and restarted the engine and the car was then okay for the next 50 miles or so. The frequency of this happening quickly increased and the distance you could drive quickly reduced!

Using VCDS again I got two error codes P1065 Fuel Pressure Regulation Discrepancy and P0121 Throttle Position Sensor Implausible Signal.

Reading up a common reason for low fuel rail pressure can be a faulty fuel pressure regulator which is mounted on the high pressure fuel pump. A cheap £18 pattern fuel pressure sensor and a new fuel filter made no difference. There was no evidence of metal shavings in the fuel filter or in the pump when I changed the FPR, caused when the bearings in the pump start to break up and also causes low fuel pressure. Another cause of low fuel pressure can be leaking fuel injectors. It was easier to start by removing the fuel injectors than the fuel pump and have them tested at diesel specialist. £120 later I was told that all the injectors had failed and all had a massive leak backs. So this is what was causing the low fuel rail pressure. £840 later and a set of remanufactured injectors and the low fuel pressure issue was resolved and all the warning lights were out.

However the tick over was still quite lumpy and the error code P0121 Throttle Position Sensor was back. So I took the throttle body off to find it was filthy! Though hardly surprising with such a high mileage. I used a plastic scraper an old tooth brush a piece of Scotch Brite and almost a whole can of carburettor cleaner and cleaned the throttle body. The lumpy tick over was still there for a few more days until it settled down and the fault code has not returned. Reading up some more what I should have probably done was use VCDS and re-coded the throttle body to return it to its factory settings to stop the lumpy tick over straight away. The throttle body self calibrates to compensate for any slight variations which it must have done when it wasn’t closing properly before I’d cleaned it, and now its calibrated itself back to where it should be.

You can turn the pipe from the egr  that goes into these to stop this happening again

Here is a well explained  How To from the forum

Yes I have seen that post. Though would deleting the EGR be a better long term solution? I've had so many cars over the years that have had EGR related issues which to me seems to defeat the whole reason for having them in the 1st place if your engine isn't running as well and cleanly as it could.