My car is idling rich when its cold. Once its warm the car has alot of problems idling. I have checked my vac lines for leaks with carb cleaner, replaced the map sensor and replaced the IAC. Could the o2 sensor be the problem? I replaced it last summer. I am throwing the low vacuum code too. Anybody have any suggestions? I am trying to get it running good because I am thinking about selling her before I leave for college next month.

 

When you turn the ignition on when cold the ECM looks at the CTS(Coolant Temp Sensor) and the TPS (Throttle Position Sensor) and determines the correct fuel/air combo for the start mode.It controls how long the injectors are turned on/off.I would make sure you have a 5 volt reference at both sensors and if thats okay then I would point my concern on the injectors themselves,might have a bad one(s).

What code number are you getting?(low vaccum)

 

You'll have to trouble shoot the low vacuum code first. If the ECm is getting a low vacuum signal, It thinks that there is a high load demand on the engine and will run it richer. This will cause both your rich when cold problem and your poor idle quality.

You have a MAP based system on your car so you'll have to either find the leaks that exist in the system, or ruling out any leaks, check out the electrical signals to and from the ECM going to the MAP sensor, since that is your vacuum measurment sensor.

The o2 sensor is not the problem since it doesn't change the fuel mixture enough to screw with the idle and isn't used when the engine is cold anyway, so it's not causing the rich problem.