1990 Chrysler New Yorker stalls

"It seems to run fine if you don't have to slow down or come to stop. It will restart and run rough then stall again"

That's the clue.

Sounds like the battery might have been disconnected or run dead recently. If so, the Engine Computer lost its memory and has to relearn "minimum throttle" before it will know when it must be in control of idle speed. It also might not give you the normal "idle flare-up" to 1500 rpm when you start the engine. To meet the conditions for the relearn to take place, drive at highway speed with the engine warmed up, then coast for at least seven seconds without touching the brake or gas pedals.

Which engine do you have?

The next thing I'd suggest is connecting a scanner that can display live data while driving and has a record feature. I use the Chrysler DRB3 but many newer aftermarket scanners have that capability too. You press the record button when the problem occurs. Since the data travels through the scanner's memory, the recording actually begins a few seconds before the button was pressed. You can play back the data later frame by frame and look for clues to the stalling problem.

Of particular interest is the "AIS Steps". The Engine Computer can set the automatic idle speed motor to any of 256 positions. The higher the number, the higher the idle speed. Step 32 is typical for a good running engine. If you find it at a significantly higher step, suspect a misfire or some other running problem. If the number is lower but the idle speed is normal or too high, suspect a vacuum leak.

Look at the "target idle speed" and compare it to the actual speed. If the actual speed is low and the AIS steps are high, the computer is trying to raise the idle speed but not having any success. The common cause years ago was that air passage around the throttle blade got plugged with carbon. That seemed to affect the 3.0L most but I haven't heard much about that lately with better fuel additives. The DRB3 also has an actuator test mode that allows you to raise engine speed in 200 rpm increments up to 2000 rpm. If engine speed doesn't respond appropriately, suspect that blocked air passage or the motor is sticking. The motor will only set a diagnostic fault code if one of the coils of wire is open. The computer won't detect a sticking motor or plugged passage.

Which engine do you have?

You will likely find it's also switching to defrost momentarily. That's due to low engine vacuum. The vacuum motors are spring-loaded to go to defrost mode for safety to insure you can see. The fix is to replace the vacuum check valve with one with a storage canister. The old one will be the size of a stack of three nickels. It's inline with a thin hard plastic vacuum hose near the firewall. The replacement is about 1 1/2" in diameter and 2" long. You can get one at the dealer's parts department, or you'll find one in a salvage yard if you check enough cars and minivans.

A common cause of heat-related stalling is the crankshaft position sensor on some engines. They fail when hot and work again when they cool down. Normally the Check Engine light will turn on and a diagnostic fault code will be stored related to that sensor.

Lower engine vacuum would result in higher fuel pressure, a rich mixture, and black smoke from the tail pipe. There's two forces acting on a molecule of fuel waiting at the injector nozzle. Think of a person about to jump out of a perfectly good airplane. There's two forces acting on them, the vacuum pulling them out and the guy behind them pushing them out. In the car, there's intake manifold vacuum on one side and fuel pressure on the other side. During coasting, vacuum goes way up. That would pull in more fuel causing a rich condition. To counteract that, fuel pressure is dropped so the net difference in the two forces remains constant. That's why there's a vacuum hose going to the pressure regulator.

A lot of the higher-class New Yorkers had automatic temperature control HVAC systems. I never got very familiar with their operation. I do know there are times when the mode will change on its own but that's the best I can tell you. When I ordered out the last of the '93 Dynastys, I ordered every option possible except the auto-temp system because I didn't want to have to worry about fixing it if something went wrong.

As for the stalling, I don't think you have a fuel pump or regulator problem. Unlike GM fuel pumps that commonly let you sit on the side of the highway, Chrysler pumps almost never stop once they're running. When the brushes in the motor become worn excessively, the motors fail to start up. A bang on the bottom of the gas tank often gets them going again for a few weeks, but once they're running, they keep running.

The pressure regulators seem to never fail. The only one I ever saw cause a problem on a Chrysler product was on a newly-delivered car that had a very long crank time to start the engine, but it ran fine once started. It simply had a cut five cent o-ring on it's nozzle that let fuel pressure bleed off as soon as the engine was stopped. GM has a lot of trouble with their regulators leaking fuel into the vacuum hose but I've never heard that about any other manufacturer.

The fuel filter isn't the cause either. They easily last the life of the car.

Here's something you might think about and compare your experience to mine. What HAS been known to happen is the pickup screen in the tank collapses or gets plugged with mud. The symptom is stalling when the highest volume of fuel is moved, which is during coasting. It takes a couple of minutes before the engine will restart. The faster you drive, the better the engine will run. I went to Minneapolis about eight years ago on the hottest day of summer. I noticed a slight hesitation when leaving a stop light; just enough to get my attention. About 30 miles later when I slowed down to turn onto a side road, the engine died and wouldn't restart. I plugged in a new MAP sensor; didn't help, but it did restart about five minutes later. Eventually I figured out it always died when coasting. Took me four hours to nurse it through the city again, then it ran fine at highway speed for 90 miles. It stalled again when I turned off the highway. The next day, the second hottest day of the year, it stalled four times in a 30 mile trip, then it was fine for the next six months. Finally it started acting up in the middle of winter. Had a couple of students look at it and they found the pickup screen plugged with a rust-colored mud. Threw in a used pump and it's been fine ever since.

Had I known what the cause of the stalling was, I could have plugged the vacuum hose going to the pressure regulator to nurse it through Minneapolis. By raising the fuel pressure, it's harder for the fuel to get through the regulator and go back to the tank, so a lower volume has to get through that screen. Because it couldn't pass that higher volume during coasting, the pressure was dropping too much and no fuel could spray from the injectors. We never did figure out why it started acting up in the really hot weather and was fine two days later when it was in the low 80s.

I overlooked this possibility because in your original post you said you already replaced the pump, but there are a lot of pumps out there that have to be installed into the original housing which means you would be reusing that pickup screen. If you got the entire assembly from the dealer or aftermarket supplier, it would have the new screen on it already.

Now that I know what caused my problem, if it were to happen again, I'd drive it with a fuel pressure gauge hooked under the wiper arm so I could see what happens to the pressure. If you have a pressure gauge, you might try that.

Your tank is probably fine. When my screen was plugged, nothing was done to clean the tank. The kids just threw in a used pump and off I went. There is a different common problem though to be aware of. You replace a dead pump, works fine for a week or two, then locks up. It's replaced under warranty, and fails again in two weeks. You get your money back, go to a different parts store, and the same thing happens. The third and fourth pumps fail in about two weeks. Out of frustration you buy a new assembly from the dealer and have no more problems.

It would appear the moral of the story is aftermarket pumps are junk, but that would be wrong. Two of those new pumps came from NAPA. They get them from the same supplier that sells them to Chrysler. Those pumps are built to very tight clearances which makes them extremely quiet compared to some other vehicles.

What we have been told is microscopic debris builds up on the impeller in the pumping chamber and locks it up. The same thing happens to each new pump until that debris is gone. That's by about the fifth or sixth pump. There was never any mention made about where that debris came from, why it was still there after running through a half dozen tanks of fuel, or whether anything could be seen floating in the fuel.

The fix was to drain the fuel and have the tank steam cleaned at a radiator repair shop before the new pump was installed. That seems to a common enough problem that many mechanics and instructors are aware of it. The symptom is the pump fails to start up which matches the other common problem of failing to start up due to worn brushes in the motor. The difference is with worn brushes, banging on the bottom of the tank will jar the motor enough for the brushes to make contact, and the motor will start and run. When debris makes the pump stick, banging on the tank won't help.

Your symptom description doesn't agree with a pump problem, and since you put a new pickup screen in with the pump assembly, that shouldn't be an issue either. Still, monitoring fuel pressure when the stalling occurs might provide a clue.