454 chevy surging and stalling

I repaired a challenging surging and stalling issue years back, numerous mechanics had looked for the problem, and couldn't find it. Turned out to be a leaky diaphram in the distributor vacuum advance. Easy test for this, simply disconnect the vac advance hose and plug it. Go for a short test drive.

Get some carb cleaner and spray along the base plate gasket of the throttle body. You may have a vacuum leak there. Also check all of the the vacuum lines to make sure honey are concnected to the proper ports. Hook up a timing light to coil wire if it has one and shine the light on the fuel cone coming out of the injector and look to see if there are big droplets of fuel mixed in. The other thing is that the minimum air rate screw may have been adjusted incorrectly. You must block the idle air control port (there is a special tool that will do that) and then set the rpm to the correct spec. (Can't believe I remember all of this). Good luck

Surging means it is running lean at idle. I would look for a vacuum leak, or the O2 sensor. I do not believe it is the idle air control valve. The reason is that the idle air control is a very slow moving device, and is not the primary control for idle speed. Normally is goes to a fixed preprogrammed position and doesn't move much. Idle speed is controlled by timing (believe it or not), as the timing can slew back and forth fast enough to make fine corrections in idle speed. But neither one is a likely cause, particularly if it runs normal at higher RPMs.

How far away is the O2 sensor? Is it 4 wires or 3? If it is very far down the pipe, and is 4 wire, that would mean it has a heater. At idle, the air may not move fast enough for it to be warm enough to be accurate. If the heater was bad, it would not work at idle, but probably work while running down the road.

If the 02 sensor has not been replaced then it's time (you won't believe the difference in power it can make). And they're cheap too.
Also check the EGR valve. To do so, unhook the vacuum line form it and plug the line off. Drive it around for a short time. If it runs better then it's time for a new one. DO NOT continue to drive without it. You will have knocking that will eventually do real damage.
Does it have an exhaust leak around the two manifold "donuts"? If so then this will cause the 02 sensor to have false readings. There is a better, metal donuts available that will last longer.

Fuel pressure regulator and vacuum lines? Have anyone cleaned the throttle body lately?

There is an idle air control valve on the right side of the throttle body near the manifold. This sort of acts like a choke. The valve can be clogged with carbon or the passage inside the throttle body can become clogged with carbon.
It is fairly easy to use some carb cleaner to clear passage and valve. Be very careful when removing the unit. It has two vary small screws that can break easily.

First thing that came to mind is a vacuum leak. Had a very similar problem when the hose came off a PCV valve. Up and down RPM at idle but going down the road wasn't really noticeable. So try replacing all the vacuum lines.

Put this into a web search.. it is quite legendary.

454 engine surging and stalling