So after replacing the battery, MAP, and TP, the van was running better for sure but it still had the original problem with a rough idle at startup and slow startup. Also there were still check engine codes being thrown about the O2 sensor not switching and running to rich. The O2 sensor is most likely working correctly as it is indicating an overly rich condition. There are a number of things that could cause a rich condition.
1. Engine coolant temperature sensor: If the computer things the engine is cold it intentionally uses a rich mixture. If this sensor is bad, it could be rich all the time.
2. Air temperature sensor: The computer uses the readings from this sensor to slightly adjust the mixture to match the temperature of the air (colder air is denser). I doubt this is the root cause the sensor is cheap.
3. Fuel pressure regulator: Regulates the pressure of the fuel going to the fuel injectors. It can fail in such as way that there is too much pressure resulting in a rich condition.
The nice thing about all these sensors is that they are cheap. Cheap enough that I am fine with replacing them immediately rather than carrying out time consuming verification procedures to ensure they are bad.
Seperately I still had the rough idle issue. This was most likely due to a dirty IAC valve. Again, a new sensor is not that expensive so I went ahead replaced it rather than trying to clean the old one, after all it would be over 20 years old by now.
I drove the car around the block after replacing all these parts. There were no codes through during that trip though I really need to drive it farther to know if the problem is really solved. Here is to hoping.
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