Hyundai Repair: 1998 Hyundai Lantra, Intermittant starting problem, air flow sensor, fuel pressure regulator

Question
Hi there, my friends 1998 Hyundai Lantra 1.6ltr Manual has occasional starting problems. It happens a couple of times a week and it doesn't matter if its cold or hot. The key operates normally and all ignition is provided and the engine will crank but will not fire. She will then turn off the ignition and wait a few minutes before trying again and usually it will start after about 5-10 minutes. Once the car is running it has no further problems. It has been looked at by a mechanic and they trouble shooted to conclude it was an electrical fault (possibly). They replaced the crank sensor, re-soldered the ignition barrel contacts, installed a new coil and uninstalled the factory immobilizer but $800 later it still has the same fault. Any ideas on what could possibly be causing this annoying problem?

Answer
Your problem could be caused by a faulty fuel pump, fuel pressure regulator, or a faulty air flow sensor or poor contact at the sensor.  If the problem occurs while the shop is checking the car, they should be able to find it.  If not, you're looking at more of the situation you're already in, wherein something is picked as a reasonably possible cause, and it may or may not repair the problem.