Delayed start

Must turn key on and wait about two minutes before truck will start. I can turn the key off and it will start right back up but if I wait about ten minutes. Then I have the delayed start all over. Truck runs good, has an occasional hesitation when taking off but not very often. I took it to a garage and they replaced the intelligent power distribution module, said they checked the fuel pressure, crank position sensor, camshaft position sensor and some of the wiring but each time before they finished testing the truck it would start up so they could never really finish what they where doing. Also, I had already replaced the mass airflow sensor and the vent canister solenoid. It keeps showing code P0448 for the purge control solenoid but I have checked it with a nine volt battery and it works and on vacuum it does not leak so I do not think that is the problem. With just the key on I can hear a high pitched whine which sounds like it is coming from either the ignition coil packs or maybe the fuel injectors. You must listen to hear it. Not very loud. I cannot really check the plugs, injectors or the ignition coils because of Nissan's bright idea to hide them with the intake manifold which the mechanic says has a labor charge of $250.00. Just to remove and put back. All dash lights and etc, work like their supposed to. Thanks, Max