For the high RPM try disconnecting the linkage to the throttle body and see how it idles, if it goes down to between 750-800 then you will need to loosen the jamnut on the linkage and turn it out maybe 2 or 3 turns. If it stays then check the throttle stop screw on the bottom in the back of the throttle body. You will have to check your TPS adjustment too right here,
MK3 TSRM On-Line
and also the next page for electrical reading.
My oil pressure guage crapped out years ago, several junkyard ones havn't worked either. Im going to check the dealer in the states in december while on vacation cause the one here can't get it. The other option is to go aftermarket with either a pod or mount or under the dash somewhere.