2001 Nissan Altima keeps dying!

#1

Engine Performance

problem

2001 Nissan Altima 4 cyl Manual 98000 miles



Car intermittently stalls out when rpm goes under about 2500 when coming to a stop or slowing down. May go for a week or two and run perfectly fine and then start acting up several times a day!

Black smoke comes out of exhaust when engine misfires.

Gas mileage

is down to about 14 mpg instead of the normal 22.

If it had a carberator (instead of the fuel injection that it actually has) you might think the float is sticking.

Code 420 (the code for cadallidic converter) comes up when engine runs bad but cadallidic converter & oxygen sensors both check out fine.

Hot weather seems to really aggrevate these problems (I live in Phoenix, AZ)

Any advice is much appreciated!!