Got a 97 Dakota SLT 5.2. Thing use to run like a beast with 200,000+ miles. Had an issue with the voltage meter on the dash reading low at idle. My head lights would dim as well. Took it to an auto parts store and had the alternator tested. Said my battery was putting out 19 volts and the alternator was bad. I replaced the alternator, I matched it up, same 130 volt alternator that came off the vehicle, (I know the Dakota offered a 90 and 130.) After replacing the truck cranks but will not start unless I give it gas. When it does start it has trouble staying idled. Battery was still reading 19 volts so I took that alternator back. Put a another one on. Now it starts when it wants to, sometimes it still needs gas and has idle trouble. Battery is now putting out 20 volts. Any idea what can cause this? I have some mechanic friends who say it is the ECU/ECM/PCM module. Some sources say they can be picked up at a salvage yard and plugged in, others say they need to be programed to your VIN. I really do not want to do more harm than good and know whats going on for sure before I get into anything as serious as the ECU/ECM/PCM. If I do need another ECU/ECM/PCM do they really need to be programed or can I just pull one from a salvage yard? Working on a limited budget and cannot afford the $600 plus labor Dodge quoted me.

 

Welcome to the forum Dakotaowner97.

The PCM needs to match the options in the truck - transmission, engine, security, etc. You can order a rebuilt online for likely less than 1/2 of what the dealer wants. You give them your info and they'll program it. All you have to do is disconnect the battery, remove the connectors, and swap it out.

The regulator is in the PCM. NOTE: You have a 130 amp alternator.

The battery is overcharging from the sounds of it. Use another meter to read the voltage, not the one on the dash. What is it engine off, at idle, and when giving it some gas.

Your lights should be VERY bright if you have 20 volts. The heater/ac fan should also be running fast. Things won't like the high voltage - and you'll also kill your battery.

 

I don't know how to test it but under the battery is a temp sensor if bad it can affect what you are experiencing. $20 for one

 

The battery temperature sensor reacts to different temperatures by producing a voltage between .04 volts and 4.96 volts DC, based on an input voltage of 5 volts DC. Because the logic module is so close to the battery, these readings can be used to estimate the temperature of the battery itself. Knowing the temperature of the battery is important because batteries are sensitive to heat, and the logic module will reduce the power sent to the battery by the alternator to prevent “cooking the battery.”
If the logic module detects a voltage outside the normal range (0.04 to 4.96 volts), it triggers a code 44 and the charging rate is set to 14.0 volts as a “safe” option. If the output of the sensor returns to the normal range, the logic module will return to normal operation and it will use the output from the sensor to adjust charging rates.

 

As for the rough running and not wanting to idle, that's pretty normal for a Dodge that's had the battery disconnected. It should be fine after you drive it a short time and it re-learns (after the charging issue is fixed, obviously).