606 is stock heat range, 605 is one rang colder, 104 is 2 colder, 103 is 3 colder. If you have made no real mods to the car, 606 is fine, if you added a few extra mods, like a smaller pulley, then go 605. I get my autolites from menards for about $2.60 a pair.
Thank you Bill, The wires are in good shape as far as a can see they were put in late last year..From reading the forums here I learned about spraying carb cleaner to check for vacuum leaks i did that on sunday and no change on the rpms..i also read about the wires touching the 02 sensor.. when putting in the spark plugs I notice cylinder 6 wire resting on the 02 sensor not the the wire and i reposition it. P0306 Misfire cylinder 6.. was my first reading and has not come back. However before me moving the wires or working on the car it had already change to P0300.
The wires are red mag xts if not mistaken..I also tried spraying water on wires with engine running and no change on idle or no sparking..Today I added Chevron fuel injector cleaner to see if that helps. I have not changed the fuel filter yet i'm wondering if this can cause misfire if clogged when punching the gas.. i'll try that next.