Stalling at random - 98 Dakota, 5.2L, Auto

This just started happening. 1998 Dodge Dakota, V8 (5.2L), Auto, 98k miles
Driving along then let off the gas. RPMs drop to near zero then come back
to life (engine stalls). Also random stalling at stop lights/signs or during low speeds with next to no acceleration. No codes showing. Also noticed that the right side PCV valve rattles and/or it sounds like a rattling or a little motor winding down towards the rear of the engine. I felt the PCV valve when the engine was turned off and it did rattle. I replaced the PCV valve today and the same thing is happening- rattling when motor is revved up then let go of throttle or shutting the engine off.
I can't seem to make it happen either. It does it at random.
Clues? Suggestions?
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Hess gas??

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It's my son's truck and no Hess gas. I haven't seen a Hess station in a very long time. I think he was using Valero. I told him to put some better stuff in and see if there is any change. The tank is low but he always runs it that way.
I took it out and couldn't make it fail. Accelerating, then stopping, then back again - couldn't make it fail or even attempt to fail. I am leaning on low or crappy fuel.
It won't run that Citgo crap for certain but it doesn't have any of that in it anyway. That crap insures failing in this manner. I used a tank of that gutless gruel a few years ago, before I knew or cared where it came from, and the truck failed every time at any complete stop. It did the same thing then as it is doing now except it was worse with that slop in it.

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Vacuum leaks?
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Good point. That may explain the PCV valve rattling when the motor is shut off. I would figure that a vacuum leak would cause codes though. Maybe not in this case. It hasn't stalled since I told him to buy better gas and more of it. Still waiting to hear from him for tonight though.

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While there is the possibility of it just being bad fuel, a more likely cause would be a failing fuel pump (which could also be caused by bad fuel). A vacuum leak (unless it is massive) normally results in a high idle speed which will set a code after a while.
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We are still looking for codes or for it to stall at random again since a different fuel was put in. So far all has been good. He was having a terrible time with the previous gas - and it was only a gallon or two at that (low). Since he put another brand in, and more than 1 gallon of it, it hasn't happened again. The other day it stalled about 20 times for no apparent reason. I am leaning on a combination of bad and/or low fuel. That is, I'm hoping that's what it was.
I'm still currious about the PCV valve on the right head rattleing when the motor is turned off. I drove that truck for 7 years and never notice that. I put in a new PCV valve and that too is ratteling. The left side doesn't rattle - only the right side and only when the engine is reved up then let go of the throttle or when the engine is shut off (quick decelleration). The PCV valve hose (right side) only goes from the PCV valve straight into the side of the intake and no place else.
What would cause it to rattle like that?
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Pressure??
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Still waiting for it to fail again since the fuel change and new PCV valve was installed.

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Well, I thought I had this problem fixed with the replacement of the IAC motor and a full tank of good gas. However, the issue resurfaced a few days after. Come to find out it was the battery. Replaced with a new one and issue has been gone for over a full week now.

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