hello all, I'm having some difficulty in diagnosing the cause of a 3 & 5 cyl. misfire. There are 200+ thousand miles on the engine. I have replaced the plugs but the code persists, code- P0122- I have inspected the boots and all but found nothing irregular. I'm leaning toward replacing the coil. Would removing and cleaning the injectors have a positive effect and should I do this first.  Any help would be appreciated.  

Yes, those are the right things to be checking for mis-fire. You should be able to ground the removed spark plug against the motor and see the spark for the offending cylinders. This will tell you if the ignition pieces are effective, wires, cap, rotor. I kind of doubt the coil is bad, else you'd be having more problems.

Two other things that cause mis-fire are bad and/or dirty injectors and burnt or sticky exhaust valve. Low compression will be the result, so do a compression test.  

Oops. 2000 was the first year for coil on plug, so it will be hard to do the spark test, sorry.

The coil packs need to be replaced as an entire assembly. I'll look up a testing procedure for you...  

Also what did the plugs for the 3 and 5 cylinders look like. Did they look the same as the rest. If the cylinder is dead you should see a difference in the plug condition.  

After poking around a bit, it seems that the best way to test the coil on plug coil is with a tester made for the job at hand.

I could not find any hints to do it at home with no special test equipment. It would probably cost you $75 to have a shop tell you if it's bad or not. A new coil pack cost $223.

So, if you had it tested and it didn't need to be replaced, that would save you $150. If it did need to be replaced, the shop would probably replace it for you and not charge you a diagnostic fee, but an install fee and maybe a parts price markup.

The wholesale price of the coil fromn the dealer is $160. Most dealer's parts guys will give you a discount if you ask.