Could be the O2 sensor, which is attached to the exhaust. Has your engine management light been on? If yes chances are it is this sensor. Careful when buying a new one as there are many different variations. Check the number and colour of wires attached to sensor.
It is idling. This is hard for an engine to do smoothly.
There could be many reasons, a vacuum leak is one possibility.
There are several things that can cause an engine to quit when you open the throttle. A poorly adjusted carburetor, and poor airflow through the air intake system are two common causes.
Your engine probably has a vacuum leak
No gas.
probably the governor going bad
A miss or A collapsed engine mount or A imbalance caused by a failing component, harmonic balancers and torque converters are common.
The #1 cause of cold air from the heater when the car is stopped, or the engine is idling, low engine coolant levels.
A car that is stopped with the engine running.
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
because of ignition coil faulty.due to mountings,abnormal fuel pressure.
Taking your foot off the accelerator.