I realize there have been plenty of 'Rough idle at cold start' posts, but I'm still not sure where to start in my troubleshooting. Below is detailed information of my problem with my 95 Grand Prix GTP (3.4L DOHC), if anyone has the patience to read it and help me track down a possible solution, I'd appreciate it more than you can imagine.
My rough idle at cold starts happens like this. I start the car after it sits for quite a few hours, which starts fine and fires up to about
1500rpm as usual when cold starting. Once it starts to settle back down, the rpm drops far too low until it nearly stalls, at which point the ecm compensates and revs it back up. This repeats continually for a short period until the engine warms up a bit, but not yet at the closed loop stage. Along with this trend is heavy vibration until it hits normal engine temperature and closed loop status. At this point, it gets nowhere near stalling, but has slow surging (rising and dropping by ~100rpm with a period of about 5 seconds).Just today, I started the car with command start. About 10 minutes later I climbed into the car and noticed the check engine light on. As soon as I started driving it disappeard. Once I got home, I threw the scan code reader on it and it showed me the trouble code was "P0131 - Bank 1 #1 Oxygen Sensor Circuit Low Voltage". The operational monitored data all looked fine at that time.
Does anyone have any idea what the problem could be? I would assume the slow surging and cold start problems are linked, but I'm trying to find out where to start troubleshooting (free steps first). I have checked my plugs and wires, and I recently (within the last year or two) replaced the egr and pcv valves, along with the fuel filter and spark plugs. I also cleaned off my mass air flow sensor, which is measuring correctly. My first guess would be to check out the IAC valve and solenoid, as well as the reading from the coolant temperature sensor from the scan code reader next time it starts that way. Any other guesses? I would really appreciate some help.
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