Engine idles up and down and then shuts off - 1996 Chevrolet Monte Carlo

have you replaced the egr valve

replace your idle air control valve that should solve problem all going well.

what size motor

I have had the same problem with my Ford mustang the only thing is that it only shuts down in high idle, after the engine temperature warms up there is no shut down. It could have something to do with the transmission or the temperature sensor the best thing to do is get a full diagnostic and not do it your self.

Vacuum Leak

Engine stalls cold or RPM fluctuates at idle up and down or dies near idle.

This problem is commonly caused by a dirty automatic idle speed control valve and throttle valve but always run a OBD2 fault code as well as the cleaning procedure. Buy a can of throttle valve cleaner (do not use carburetor spray cleaner!) from NAPA or Carquest (made by CRC chemicals) and spray it into the air intake while the engine is running, use up about 1/2 the can, engine will try to stall hold the speed up, shut it down and let it soak for 30 minutes, restart and blow out the remaining fluid, shut it down and disconnect the negative battery cable for 5 Min's to reset the base idle control

Engine stall or RPM fluctuates at idle.

This problem is commonly caused by a dirty automatic idle speed control valve and throttle valve. Buy a can of throttle valve cleaner (do not use carburetor spray cleaner!) from NAPA or Carquest (made by CRC chemicals) and spray it into the air intake while the engine is running, use up about 1/2 the can, engine will try to stall hold the speed up, shut it down and let it soak for 30 minutes, restart and blow out the remaining fluid, shut it down and disconnect the negative battery cable for 5 Min's to reset the base idle control

IDLE SPEED COULD BE TOO LOW.IDLE SPEED SHOULD BE 800 RPM. IF IDLE SPEED TOO LOW AND ENGINE NOT WELL TUNE UP AIR CONDITIONER WILL PUT LOAD ON ENGINE CAUSE ENGINE OVER HEAT AND SHUT OFF.

The noise is caused by the engine running on after the ignition is shut off. It makes noise because the pistons are rattling in the cylinders from incorrect timing. This has nothing to do with the mechanical or electronic timing of the engine. The engine runs on either because of hot glowing carbon deposits in the cylinder head or because the engine was shut down when it was running too fast. Sometimes the carbon can be literally blown out by running the engine at high rpm for a short time. Put it in second gear and run it for a couple of miles on the highway. If this does not work the heads will have to be removed and the carbon cleaned out manually. The shut down when running too fast problem can be caused by the idle being set too high or by shutting the engine off before it has reached idle speed. If you can adjust the idle speed try reducing it. If not always hesitate before shutting the engine down to let it reach idle speed. Good Luck!

If the car is having trouble maintaining idle (the tach dips and car dies) the common causes are the idle control valve and camshaft position sensors. The cam sensors failing will be indicated by a check engine light.

The ICV can removed and cleaned with good results (I think there is a write up on bimmerfest) or purchased new for about $100.

While you are in there check the intake boot that is Y shaped for cracks, it's prone to fail and will mess up your idle too.

read up on the major forums and you'll get more info