You may have two separate issues. Idle speed fluctuates: Check the entire air intake [complicated name for where air enters usually through a black oval tube, enters the air filter and then the engine]. Look for breaks in the plastic, or cracks, or parts that weren't assembled correctly. This lets ambient air in and the fluctuating idle is the computer's attempt to adjust the fuel and air mix to what "it". the computer, knows it should be. This is a good sign as it tells you expensive parts are working. Spring for a new air filter element from an auto supply store while you are at it.

Transmission: Check the level of the auto trans fluid. Car parked level. Sometimes two marks, one for cold engine and one for hot engine. If no record of auto trans fluid service have the fluid and trans filter [if so equipped] drained and changed. DON'T do a flush!. Be certain to use Toyota spec fluid. Don't rely on a mechanic to know what it is, read the manual or ask a dealer. There is a difference in trans fluids.

if the rpm gauge is sticking or not working. focus on the engine sounds, the gauge can lie. if the engine is bouncing up and down on idle and the mechanic has fixed this before but it came back then id have to assume he thought the idle air control valve was faulty and he probably just cleaned it hoping it would fix it cause they do get dirty and tend to stick. so id assume he tried to fix it but just cleaning it was not enough. but there is so much that could be wrong by all that you described. anything from sensors to even possible fuel filter clogging up. its hard to pin point the problem without looking at it.....

with this type of problem it is common for a check engine light to be on... if it is go have the code read at a automotive store.. they do it for free.

Well, my recommendation would be a transmission service. Cause the gears getting stuck comes from the gearbox. Cause I have a simmilar problem, and I just keep on trying till I hit it

:(

I drive a 98' Toyota Camry CE and the RPM fluctuates between 0-1. It bounces and makes a "voom voom voom" noise. When I'm driving and I'm in idle sometimes it gets stuck under 2 on the rpm and the car doesn't move then I have to shove my foot to the floor and then it moves. But the rpm getting stuck and the 2 as well are both problems of each other. My nana has it "fixed" by the same guy she's had for a while, but obviously I need to go somewhere else, BC this is the second time. She just gave me this car. Is this something expensive or just a belt or something? Thank you.