Hard to start when engine is cold and emits lots of white smoke

[bagassto_ok]

My 95 nissan maxima doesnt start when engine is cold. I have to press accelerator for minutes to warm it up. At that time when I lift my foot up, the engine tries to stall and shut off and it gives lots of white smoke and smell of gas. I replaced the Mass air flow sensor to the new one yesterday and its idle was increased to 800 from 400 rpm and it started really easily. The stalling happened again today. Some mechanic suggests to re-flash the ECU unit. I am not sure it helps or not but I would like to have some confirmation before doing that because the cost is not inexpensive...

If the problem comes from ECU unit, can I replace ECU with the used one instead of paying lots of money to the dealer?

Any solution or guessing would be very welcome because I want to be sure before doing anything.

Thanks

[loystock]

Welcome to NICO.

Did you clean the MAF sensor connector when you replaced the sensor? If not, use zero-residue Contact Cleaner or MAF Sensor Cleaner on the connector pins and sockets, then apply dielectric grease before reconnecting. Also check tightness of air intake connections and vacuum fittings.

The ECU has a learning capability. Just drive the car on city streets for several minutes and then on the highway with several WOTs (no need to overspeed).

You may have 'ghost code' so better to have the car scanned for free at Autozone.