Stalling when slowing down

There are two common things to look for first. One is when you replaced the fuel pump, did you install a new pump into the original housing, or did you replace the complete housing assembly? There is a strainer on the housing that can become plugged, but unless a new one came with the pump, it only gets replaced when you put the entire housing in, (or if you buy the replacement strainer). One of the clues to a plugged strainer is the stalling typically occurs when the largest volume of fuel is being pumped, which is during coasting. That does not always apply to vehicles with the fuel pressure regulator inside the gas tank, but it does to those on the fuel rail.

Next, before you go looking for the hard stuff, most of what you described can be attributed to recently disconnecting the battery or letting it run dead. The engine computer will relearn most of its data without you doing anything or even being aware of it, except for "minimum throttle". Until the computer relearns that, it will not know when it has to be in control of idle speed. Common symptoms are the engine will not start to run unless you hold the accelerator pedal down 1/4", you will not get the nice "idle flare-up" to 1,500 rpm at start-up, and it will tend to stall at stop signs. To meet the conditions for that relearn to take place, drive at highway speed with the engine warmed up, then coast for at least seven seconds without touching the pedals.

I can see why I may have caused some confusion. After looking up the fuel pump for your application, there are some noteworthy differences from what was used in the past. First, I could not find the less-expensive pump and motor that you have to stick into your existing housing. Only the complete system with the pump already in the housing is available. Next, the common strainer that likes to become plugged isn't readily visible. Normally it is a mesh sock hanging off the bottom of the housing. For yours, it must be encased in the bottom of the housing and is not replaceable separately. Putting the filter and regulator inside the tank is also new with this design.

Once you do the relearn, if you are still having issues with low idle speed, it will help a lot if you can obtain a scanner so we can look at live data. The item in question in this case is the number of "idle steps" the computer is requesting. The scanner should also give you the ability to run idle speed up and down to test the idle control system. I have a Chrysler DRB3 for all of my vehicles. A lot of independent shops bought them because with an extra plug-in card, they can do emissions-related work on every brand of car sold in the U.S. Starting with 1996 models. This scanner started becoming obsolete in 2004 on the Dakota/Durango, and the last it worked on was some 2008 Jeeps. For that reason, many of these shops are happy to sell their scanners to buy something that works on newer vehicles. You might ask at a few local shops if they have one of these to borrow or sell.

Dandy.

Diagnostic fault codes never say to replace a part or that one is bad. They only indicate the circuit or system that needs further diagnosis. Also be aware there are over a dozen fault codes related to speed sensors and they mean very different things. We need to know the exact fault code number to know where to start the diagnosis. We can interpret them for you, or you can go here:

https://www.2carpros.com/trouble_codes/obd2

To see the definitions.

P0500 - Vehicle Speed Sensor Malfunction

Nope. You are interpreting that incorrectly, but I can see how this is easily possible. A more accurate description would be "vehicle speed sensor circuit malfunction". It could indeed be caused by a defective sensor, but there is a fifty percent chance there is some other cause. This same code will set if any of the wires to the sensor are cut, if the signal wire is grounded out, (such as on your parking brake cable), or if the gear that spins it, (on older models) is stripped or broken, if metal filings are stuck on the tip of the magnet, (for your style of sensor), or if the air gap between the sensor tip and toothed wheel is too big. No fault code has ever said to replace a part. Experience will eventually teach you that you'll see the same pattern failures many times for some car models, and some of those will be sensors that fail so often, we jump on them without bothering to do any testing first, and 99 percent of the time we'll be right. It is that one percent, or the intermittent ones that come back to bite us.

The engine computer also performs a constant test of the integrity of the circuit wiring. In the case of metal filings on the magnet tip, that would stop the sensor from generating a signal, and you would get code 500, but the electrical circuit would still be fine. The sensor would simply be saying the vehicle is standing still, but the computer knows that is not right based on other criteria, particularly high intake manifold vacuum for an extended period of time when you're coasting. It knows you are coasting, so it knows you have to be moving, so it knows it is supposed to be seeing a speed signal.

Wonderful. Please keep me posted on your progress.