1999 Chevrolet Malibu stalling while driving problem

By now you should have figured out that replacing random parts is the most expensive and least effective way to diagnose a problem. If not, you need a more accurate dart board. None of the parts you mentioned will affect an electrical problem with the dash board. One thing you can do yourself without a scanner is to follow the smaller positive battery wire to the under-hood fuse box. Be sure that connection is clean and tight. Follow the smaller black negative wire to the body and be sure that one isn't rusty.

You might also want to have the charging system tested, in particular for maximum output current and "ripple" voltage. If those are suspect, the generator is a common cause on GM vehicles for elusive engine running problems. I can explain that in more detail if it comes to that. For now, the test must show that you're getting in the area of 90 to perhaps as much as 120 amps. What we don't want to see is exactly one third of the maximum rating which is around 30 to 35 amps.

Dandy. The charging system problem I'm concerned with requires a professional load tester so you'll have to visit a shop for that. Due to their design, starting with the '87 models, these GM generators develop huge voltage spikes that can damage the internal diodes and voltage regulator, and interfere with computer sensor signals. The battery is the key component in damping and absorbing those spikes, but as they age and the lead flakes off the plates, they lose their ability to do that. It is common to go through four to six replacement generators in the life of the vehicle, but to reduce the number of repeat failures, replace the battery whenever the generator has to be replaced, unless it is less than about two years old.

When one of the six diodes fails, you'll lose exactly two thirds of the generator's capacity. 30 amps from the common 90 amp generator isn't enough to run the entire electrical system under all conditions. The battery will have to make up the difference until it slowly runs down over days or weeks.

Those voltage spikes also radiate into other wires magnetically and cause weird signals to show up as sensor signals. The Engine Computer can interpret those as legitimate signals and try to run on them. That's where those elusive running problems come from that defy diagnosis. One trick to identifying them is to disconnect the small plug on the side / rear of the generator to disable it. If the running problem clears up, the charging system should be tested.

You can start the testing on any charging system by simply measuring battery voltage with the engine running. It must be between 13.75 and 14.75 volts. If that is okay, it just means the rest of the tests will have validity. The first thing the load tester will do is draw the maximum full-load current to see how much can be developed. That is either going to be very near the generator's rated current or one third of that. If it's one third, one of the diodes has failed and the generator must be replaced. It's not practical economically on other brands to replace the diodes because rebuilt generators aren't that expensive, but on GM's generators it is nearly impossible to do so without destroying other parts when trying to get them apart. These generators weren't designed to be repaired.

AC generators have three-phase output. When one phase is missing due to a failed diode, "ripple" voltage will be very high. That is also measured by most professional load testers. Some show it as a voltage, and others use a bar graph to show relative voltage. That can't be measured accurately with a digital voltmeter. You'd have to use the AC voltage scales and those are only accurate at 60 Hz as in house wiring.