1995 E-320. I'm not sure what's going on, but here are the symptoms. First off, I noticed a subtle whine, I traced this to the power steering pump and suspect the bearings are on their way out. Whether this is related to the following issue, I don't know, it just happens to be going on concurrently. perhaps there's friction on the bearings causing the following issue? don't know.

second, occassionally the engine RPMs surge up and down, not drastically, maybe 300 or so. Not really bucking but a gentle surging of the engine. this doesn't happen all the time. when surging the engine is still smooth, not choppy or rough. I suspected a vacuum leak, but cruise control and door locks work, pushing the brake doesn't seem to affect this, or be squishy or any different than normal. engine oil level was high, so I changed the oil which seemed to have helped a bit, but not totally. meaning it still happens, just not as often. there also seems to be a slight loss of power while this is happening. It's an intermittent issue, no issues yesterday or this morning, but the day before on the drive home it happened, but only for about five minutes. the engine light did come on, I haven't downloaded the data yet.

could this be a fuel delivery issue? O2 sensors? bad spark plugs? manifold leak? or perhaps the PS pump is causing this? I'm at a loss!