What's your voltage? A computer running in emergency mode might run rich, and fail to leave a code?
When I was young I bought a minivan for $500... found out a LOT about cars!
Once a neg. battery cable got loose on me and the car died for no reason, then restarted fine, only to die again. Might be worth it to check physical connections of underhood components, ESPECIALLY where the alarm work was done.
SEARCHING FOR A NEW MUSTANG!!!!!!
Last Mustang - 2012 Kona Blue/Stone Top-Interior V6/AT convertible. Panavise Phone Mount.