It is over charged and builds to much pressure on the high side when the engine is at a higher RPM. Need to remove some feon.
Perhaps the A/C is drawing too much power from the engine, could be the engine is idling too low.
air leek
It is the idling sensor on top of the intake
get an engine diagnostic check, a lot of different problems can contribute to your situation.
If you mean why the difference in RPMs between idling and driving, the difference is due to the engine load; At idle, the engine isn't really doing much other than staying running, but under load (driving) the engine has to put its power out to the drivetrain, hence the symptomatic loss of engine speed (RPMs).
Your thermostat is stuck open. Buy a new one they are usually really cheap and you can usually repair it yourself. They are easy to get to even in compact engine space.
A car that is stopped with the engine running.
Yupp Clogged fuel filter. Hole in the gas line.
Check coolant level Cooling fan working? Dirt or clogged radiator? Defective radiator cap?
In order to tell you that you would have to describe the noise and what the car is doing when the noise is made. Are you idling, driving, just turned the AC on? What is occurring and what is the noise? Idling and sounds worse when AC is on. Sounds like it is coming from the top of the engine. Vehicle has 120k miles
Thermostat? or radiator? Greg
An engine revving to high RPMs could be a symptom of many conditions. The potential cause?æalso depends on whether this happens?æwhile idling or while driving.