'94 Toyota Camry

OK, so I have this car and it has 135K on it, no big problems. Last year I saw that when I took it out on the highway, the RPMs at 65mph would be around 3.5k. I took it in and the service guys, whom I trust, said it was soething to do with the throttle-plate (or something) not closing. I had them fix it, and things were fine.



Until now. It’s doing it again. I’ll be out on the highway and the RPMs are up there again. I get off at an exit, come to a full stop, and get back on the highway again, and it’s OK, back down to around 2.5k RPMs at 65 mph.



This happens whether the car is just started, or when I take it to the store, do my shopping, and come back out-- in other words, the engine isn’t stone cold.



How does the throttle thing get broken again in a year? Or could it be something else? Is the car safe to drive if I just keep an eye on the RPMs?



We maintain the car well; it gets an oil change several times a year and the tires rotated and all. I try to take care of problems right away, but I want to know a bot more about what’s going on here.

Check your maintenance receipts to see when the transmission was last serviced.
For that matter, have you checked the level, the color, and the smell of your transmission fluid recently?

If I recall correctly, this model should have had a trans fluid and filter change at 90k. If that was not done, that could be the origin of the problem, which sounds like it is transmission-related. For that matter, did the car have its major 90k service (and the subsequent 120k service) performed?
Please note that these services typically involve much more than oil changes and tire rotations.