Help "check Engine Light"

[shadi]

Hello,

I have lexus ls 400 model 1994,

it runs okay,

once "check engine light" comes on

1- tranmission problems.

2- AC is off.

3- car turns off once it stops.

4- it's power became very weak.

5- black gas from the exhaust.

i was expecting it's sensors problem.

should i change the computer.

sorry for my poor English.