In my opinion it's easy to swap in a new fuel pressure regulator before diving into the tank.

I just did another check: 30psi didn't change with press of gas; but it did change if I unplug the vacuum line on the fuel pressure regulator: it increased to 40psi. But this 40psi won't change if I press gas.

Does this mean the pump is broken? Thanks!

With the vacuum hose disconnected you are getting as much fuel pressure as the regulator allows. Usually this is 42-45 PSI, but your gauge looks like it is reading a little low. This is the same as running wide open throttle (WOT). i.e. no manifold vacuum. So blipping the throttle with the vacuum hose disconnected should not change the reading. If the pressure decreases, then you have a bad pump. Right now I would say your fuel pump is okay.

The true test is driving down the road and observing the fuel pressure under load. If you go down this path, take someone along to be the observer.

And once you are done with this validation you will most likely still have the rolling idle issue.

Yes, I know it's low but not too low. Since I bought one cheap already, I just replaced it. I also noticed one thing: the old one draws about 1A current and noisy, the new one draws 3A current and quiet. Because this big difference, something is wrong.

I also found the fuel pump was assembled wrong from factory (I am the original owner and nobody ever touched it). I will post a picture to show.

Thanks!

That hole on the float is supposed to be mounted with the screw, but it's not. It's hanging there with no place to attach to. This is the original pump.

Here shows how I did it when I install the new pump. I will put the tank on tomorrow and let you know the result.

Looks like someone missed the hole......

Since it came from the factory, I think it's Ford supplier's problem. But there is still a screw head mark on it... I have no idea what happened there.

After install the tank back, the good news is the RPM is stable now, doesn't oscillate anymore. But the bad news is it's still a little bit low, about 500 and stays there. So the engine is still shaky as a result. I hope after driving a couple of days, it will correct itself.

I also measured the fuel pressure again. All the readings are the same as before, 30psi idling, 40psi with vacuum removed. But the readings are stable because the RPM is stable.

So I think the fuel pump is partially to blame for the problem but may not be all.

I am still trying to fix this rough idle problem on my Bronco. Here are what I did recently:

1. Measured compression on all cylinders:
https://cimg6.ibsrv.net/gimg/www.for...b17b9f4d61.jpg
all look normal;

2. Replaced all vacuum hoses:
https://cimg8.ibsrv.net/gimg/www.for...0dbcb4b3e5.jpg
instead of the original hose connector, I made direct connection of all;

3. I found a port which is not connected to anything at the far end of the engine (is this normal?):
https://cimg9.ibsrv.net/gimg/www.for...4c5421e996.jpg

After all these, the idle is still rough and no change at all!

Anybody knows what I should do/check next? I am thinking flush/clean all fuel injectors...

I would plug that port.

I tried to use finger to plug it when the engine is running. I didn't feel anything and the engine didn't change anything. I will find a cap for it. Thanks!

Usually that top port of the PCV is not open to atmosphere. The rubber grommet in the valve cover where that PCV plugs in, below the L shaped hose is known to shrink and become an effective vacuum leak.

The brake booster is also a common source of vacuum leaks too.

One other item to contemplate is the throttlebody. The blades get worn, the butterfly shaft gets worn and gaskets age. This is one of the most common areas of vacuum leaks and the rolling idle issue.

It's a process of elimination.

Thanks! I will check all those this weekend...