Backfire though intake

[ARTHUR, KEITH]

Hello.
My 1991 90 is having a few problems.  I guess it decided i didn't spend enough money on it over the summer. 
The Symptoms.

1) It takes a long time to start after it has been sitting.  It will start up immediatly if you try within a few minutes of it being turned off.  In the morning will will crank over for 8-12 seconds.  The temp is about 70 degrees F.

2)  If you open the throttle quickly it will backfire though the air intake.  I hear a small pop and then hear the air meter plate being slammed down and bouncing up.  After the car has been running for a few minutes it is fine.

3)  Very randomly it will idle at around 200 rpms and the voltage drops down to 11.5  If the car is turned off and restarted it idles normally.

My 90 has new 5 new injectors, seals, and seats. New oxygen sensor, spark plugs.  The cap, rotor and wires are all fine. It also has a new battery and alternator brushes.

please let me hear some ideas.
peace
keith