oil temp gauge

I bought my 2000 a4 1.8t q recently and on a recent drive from Michigan to Colorado I noticed problems with the oil temp gauge running all over the place it will be at 175 then the next minute it will be at 325 and then will sink to 200. All this happens within the space of a minute, and it does it the whole time. I have checked the oil temp manually and checked the back pressure from the exhaust to see if it was overheating the turbo but they are right on the money so it in't a mechanical problem. Since this started happenning the boost has gone from 16psi to between 5 & 8 psi, which I figure the com has shut the wastegate to lower the boost because of the temp irregularities. I have checked and there is no oil sludge problem. My theory is that it could be a bad ground because the guy that had the car before me installed a turbo timer and I have looked at the wiring job and it's a bit bohemian, or the oil temp sensor has gone bad.

Just wanted some opinions before I started pulling stuff off, has anyone seen this before??