rough idle and hesitation

[blitz23]

I have 1985 Nissan S12 200sx turbo. I have a problem with rough cold idle and stumble when the engine is cold.

After the warm up period, the car run rough and stumble only when the engine is cold. after it's been warmed up it's fine. the simptomps are :

1. when the engine is cold, if I give a gas it seems like it doesn't get it and then all the sudden it'll get and lurch forward with power. I've been told that this could be MAF problem. it some time stumble/hesitate under boost.

2. I have a boost gauge, and when the engine is cold, the boost gauge show a vacuum leak at 14 in-hg where a normal engine should be at 21-22. But, when the engine is warm everything is normal. it idle low and has no power if the vacuum gague still show 14.

I have brand new O2 sensor, and didn't change anything in the process or putting in new turbo and exhaust. CA-DET T25 and 3 inch turbo back. MSD Blaster SS coils.

I have narrow band installed and it shows that it runs rich most of the time, even when idling. it will run stoich when crusing on the highway.