Engine idle surges up and down when stopping at lights

The item on the end of the fuel rail. The name escapes me. Help me folks.

Heisenberg wrote:
The item on the end of the fuel rail. The name escapes me. Help me folks.

Fuel pressure regulator?

Does the surge occur all the time at idle, or just occasionally? Otherwise does it run normally? Does it matter if the air conditioning is turned on or off?

IAC valve.

Fuel pressure has been check and is good. IAC has been replaced. It happens with the a/c on and off. The surge occurs a lot engine stalls occasionally
Sorry to answer all questions at once but I don't know how to answer questions individually

Does the surge happen more often when coming off the highway to a stop?
I have seen issues with cars in the past where the EGR valve sticks partially open and the engine runs rough or stalls after cruising down the highway.

If your engine has an EGR valve and if it's accessible try this. When you come to a stop and the surge is happening, pop the hood and tap on the top of the EGR valve with something heavy like a small hammer or a big wrench. If the there is no change then the EGR is probably not at fault. But if the surge stops then get the EGR valve looked at or replaced.

With gas engines, surging is sometimes due to a vacuum leak.

My 1988 Explorer did this and the cause was a cracked intake manifold. It was sucking unmetered air.

A dirty or faulty mass air flow sensor will cause this issue IIRC and not always throw a code.

I will check the mass air flow sensor
Thank you