Fuel Pump problems of the 1998 Mazda 626

Since approximately June, 2002, the immobilizer has been turning off the engine immediately after I start the car, even though the alarm is deactivated. I usually have to wait 24 hours or so for the alarm to reset itself. This occurs every 2 months or so, but when it happens, it continues to occur for several days. It has happened even when the car wasn't locked. June, 2002, replaced battery; Dec. 2002, installed new fuel pump; Jan. 2003, installed fuel pump again; April, 2003, bought new key and clicker; sept. 2003, dealer wants to replace immobilizer @ nearly $800. All of these repairs are at dealer's request, and are interspersed with many tows and alarm resets.