What is the normal RPM when driving 55mph?
My 1997 3.0L LX runs at just under 2000 RPM at 55mph. But, it 'sounds' like it's 3000 RPM, in that it's noticeably more 'hummy' now. Not sure what that's about. Is there a chance the O/D button got pushed accidentally (and it's not in O/D now)? If so, that still wouldn't explain it showing 2000 RPM (which sounds about right and shouldn't sound revved up).
Should be around the 2K mark. You might be experienceing other noises not associated with the transmission. Does it only make the noise traveling down the road or at idle as well?
Possible and not unusual is the failure of a Motor Mount or two. That will transmit noise throughout the car that you never heard before. Does it "clunk" when you put it in Drive or Reverse from a stop?
No, there is no clunking when going between drive and reverse and stop. Could it still be motor mount failure? And it really only makes this louder than usual hum on the highway; although I do notice that when I'm coasting, say, in town at around 30mph, the car doesn't slow down like it used to. It seems to like to hum along now at 30 (not slowing down until I brake). It's like it's thinks my foot's on the gas keeping it at 30 when in fact my foot's not on the gas at all. The alternator recently had to be replaced. Maybe the mechanics messed up the tuning of the car when they replaced the alternator?
They can't mess up the tuning of the car. The computer did reset and has to re-learn several settings since the battery was disconnected but everything should be back to normal within a few hundred miles. Perhaps you should take it back to them and explain what you are experiencing. Motor mounts can still make strange noises but so can many other things. The IAC (Idle Air Control) can fail and cause symptoms like you mention but that's only a guess.
Something isn't right, I'd take it back to the mechanic and have them check it out.
I found out that there were 2 issues going on with the car. The "not slowing down with foot OFF the gas (at 30mph)" issue was the result of a malfunctioning fuel intake regulator (I guess it had runs its course after 140K miles). And the "humming (at 55mph) as if the RPMs were 3000, when in fact they were at 2000 as correctly displayed on the RPM meter" issue was a results of the right front wheel bearings being shot. So, replacing the regulator and the bearings corrected the two problems.
I'm glad you got it fixed. Take care!
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