I need help - the timing is off on the truck, and my mechanic checked it out. It's idling about right (a little over 1000 rpm), but it idles lousily. If I turn on the A/C, the car starts shaking, and sometimes just die. My Mechanic told me I might need to have my distributor changed - but he didn't do anything else to adjust the timing. He just increased more air flow (adjusted the air/gas ratio). Is he jerking me around? I'm reading up on the truck right now, but I could really use some help from you pros out there. Where should I adjust the timing? What should I do. Please help.