Nissan Repair: 96 Nissan Maxima - hard starting / rough idle, intake plenum, vacuum leak

Question
Car was running well.  Removed intake plenum to repair leaking valve cover.  Put everything back.  Locked myself out of the car.  Opened the lock with coat hanger and set off aftermarket alarm.  Disconnected main box and disabled alarm.  Car now only starts with starting fluid at wide open throttle.  Engine will race at WOT, so I have to let off the gas, then below 3k rpm it will want to stall, so I have to bring back to WOT to keep it running.  While running, it backfires through the intake.  Ignition spark is good.  Verified 12 volts going to the MAF, TPS, fuel injectors, ign coils.  Fuel filter is clean and had fuel.  Tested fuel pressure at fuel rail at about 35-40 psi.  I don't know where to look and would appreciate your help bigtime.  I have tools, space and a little auto knowledge and can continue testing/diagnosing with your guidance...and can reply to you with results.

Answer
Quoc,

Sounds like a massive vacuum leak.  Either the intake gasket, throttle body gasket or a hose is off causing a massive vacuum leak.  Thus, you need to have your foot on the throttle to give it enough gas to compensate.  I would verify the alarm is not cutting spark or soing other strange things.  Usually, an aftermarket alarm is set with a relay that cuts power to the starter.  So,, you should be ok.