Chevrolet Repair: chevy van intermittent misfire, chevy g20 van, chevy dealer

Question
I have a 1993 Chevy G20 Van. 5.7 liter V8
The problem is: Most of the time the van runs fine but intermittently it will begin to act up and almost stall out. If at an idle when this is happening, the rpm quickly drops down for a few seconds and then recovers quickly. It may do this for a short duration and then return to normal operation. If you are driving down the road and this starts happening it will act in the same sequence and jerk like the engine is trying to shut off. I made the mistake of taking it to a shop, because of the need for a quick repair and they rebuilt the distributor and after $700 it was still acting the same. I learned my lesson there the hard way. Since then I have replaced the in-line fuel filter. No change in symptoms. It started acting like this about a month to 6 weeks ago. I have tried to narrow  it down to a certain time that this happens. It is not dependent on whether the engine is hot or cold it can happen at both times and varies in when it will occur.
I have inspected the engine area for any hoses disconected or obviously worn. Nothing apparent.
I am trying to figure out what direction to go from here. It almost acts like the fuel is momentarily being shut off.I also would like to mention that about a year ago the fuel gauge became inaccurate and at times will stay indicating near full even though the tank is getting low. I am wondering if there is a possibility that there is contamination in the tank. I would appreciate any advice on what to check before going toward removing the tank and how I could verify if the fuel is being delivered correctly while this is occuring. I check the on board diagnostics and no abnormal DTC was indicated . It flashed DTC 12 , which indicated no monitored failures we stored.
Any help that you could give to me would be greatly appreciated.

I have a Chevy dealer repair manual and it references checking the sensors using a Tech 1 tool. Is there other acceptable ways to check the various sensors i.e. the MAP Sensor, the O2 Sensor, the TPI Sensor, etc.?



Thank you,

Dan

Answer
Hello Dan,
Most of the sensors can be tested with a good digital ohm meter. Like the TPS needs to just show a good gradual change in resistance throughout its travel, and do so consistently.

Your problem could be the EGR valve opening and sticking occasionally.

I like to connect a fuel pressure tester, and leave it connected while I drive, just to see if the pressure drops, causing the stumble, or if it stays up to spec till after the engine dies. 13 PSI for yours, I am relatively sure.
If there is some water in the fuel tank, it will cause that problem when it is sucked in.
And water, or no fuel pressure, there isn't a code for.

Van