When an engine is over revving it could be due to wind resistance or a bad or slipping transmission or worn out clutch and pressure plate for a manual transmission.
Dirty or bad fuel injectors, bad ignition control module, bad idle air control valve etc can all cause engine over revving.
On some vehicles the engine may rev high for a few minutes when first started but then it should slow down in idle.
If not it could be the idle air control valve or the ignition control module failing.
Wind can affect your engines RPM as when it's windy and you're driving you need to use more engine power to overcome the wind speed.
It's normal for your RPM to increase some when you're trying to drive into and against wind especially if it's blowing hard.
My trucks RPM will go up pretty high when I'm driving in wind of 50 MPH or above as the engine needs the power to overcome the wind pushing back on it.
Your vehicles RPM can jump up while driving for a variety of different reasons such as driving in windy conditions, bad or slipping transmission, bad sensor for your RPM gauge, Worn out Spark Plugs, Dirty Air filters, Vacuum Leaks, Dirty Fuel Injectors, bad Fuel Injectors, bad idle air control valve.
When your transmission goes out what happens will depend on whether it's an automatic transmission or a standard transmission.
If it's a standard or manual transmission then the gears may start grinding or it may not go into gear or it may take higher RPM to get up to speed.
For an automatic transmission the transmission may start slipping and the RPM go up while you're speed is not increasing.
Or you may notice noises from the transmission or the transmission may not shift into forward or reverse at all.
When your transmission goes out, your car's handling will be affected.
You may experience vibrations, slippage (engine revs but vehicle does not accelerate as it should) or different shift patterns in your vehicle.
The gear shift on your car will stop working when the transmission dies.
What causes a transmission to go bad?
Low automatic transmission fluid, one of the most common causes of a slipping transmission, reduces the hydraulic pressure necessary to properly shift.
If there's not enough fluid or it is starting to lose its effectiveness in lubricating and cooling, the transmission will perform poorly or stop working altogether.
The signs and symptoms of a bad and failing automatic transmission is taking too long to shift, the RPM's going up but vehicle doesn't gain speed, burn transmission fluid, transmission slipping, whining or clunking noise.
If you notice that your vehicle takes more than a few minutes to shift into the next gear while accelerating then either your transmission fluid is low or you have a clogged transmission filter or the transmission is about to go out.
The transmission when it's working properly should respond within a few seconds to the changing of gears upon acceleration.
So it should almost immediately shit up into the next gear when you accelerate and the RPM's go up and if not something is not right.
Sometimes it's as simple as low transmission fluid, dirty transmission fluid or clogged transmission filter.
Then other times it could be the automatic transmission going out.
If it's a manual transmission then the gears could be grinding when you try to shift it or you notice clunking or grinding gear sounds when accelerating.
If you have a transmission temperature gauge and it goes up way too high then you have a transmission problem that needs checked out.
An automatic transmission should last 160,000 to 300,000 miles and sometimes more depending on how well you care for it.