My 98 Cadillac Catera RPM gauge will go up but will not come back down. If I push the RPM neadle back to 0 with a piece of wire through the odomiter reset button hole, it will jump up a little at a time when the car is running and not come back down at all. Do you know the cause? Do you know where the gauge sending unit is on the engine that tells the gauge the engine speed (RPM's)? Do you know where I can get a repair manual?