I have a 1995 Oldsmobile 98 sedan with engine braking problems. It has the 3800 engine (complete with a slight intake manifold leak, as per the GM custom) and low miles. I recently moved from the midwest to the west coast, where this battleship encountered real mountains for the first time on the road trip west. Driving into Yellowstone NP from Cody, Wyoming I encountered a particularly hilly stretch of US highway that had a steep grade and plenty of curves down the hill. I took the car out of overdrive and put it down a gear to let the engine braking assist. Nothing happened. The car continued to speed up with no assistance from the engine, even in 2nd, which should have held me at around 45-50. To test this on the next big drop, I started at the top from a full stop, and in first gear. I should have been walking down the mountain, but instead the car kept speeding up to around 40 and 4000 rpms before I relented and shifted up.
Is this a transmission problem? Or would the lack of engine braking downhill but no transmission problems when tooling around town elsewhere indicate something else? Maybe a vacuum leak?