Car is a 1990 ls400. Problem only exists when it is chilly out, maybe 55 F or lower. On startup, the engine sputters and idles low and emits white smoke from the exhaust. After about 20 to 150 seconds, the idle abruptly becomes normal again. The lower the temperature outside, the longer it takes to become normal.
I think it is not getting enough fuel because pressing the throttle a little does not make the problem go away. Also white smoke is indicative of a lean condition. The rpms do raise when I press it, but still sputters. The abruptness of the change leads me to think it is a signal based issue, not a plugged injector, fuel filter etc.
What could be causing it to not get enough fuel when it is cold out?
Possibilities could be
1) Intake air temperature sensor - reading the air as warmer than it is, therefore not sending enough fuel to compensate for the denser charge. I know this is part of the MAF assembly.
2) Mass airflow sensor - not sensing as much airflow as it should and lacking fuel, I know I have the Karman-vortex style MAF so cleaning is not an option.
3) Air leak - but wouldn't that problem exist at all ambient air temperatures?
What else could it be? The thing that confuses me is the way it abruptly fixes itself. It seems like the ecu is getting feedback from the oxygen sensors and compensating once they get warmed up. I just want to see if anyone has any insight on this phenomenon before I buy 5 parts and fail to solve the problem. I already replaced both main oxygen sensors recently.