Q: Check engine light on, rough idle/run except with a/c on 2000 Toyota Tacoma

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Check engine light on. Recently (i.e. a couple of months ago) my truck started to run and idle rough, first it was most noticeable when idling then I noticed how it got rough running also; the funny thing is, when the a/c clicks on, it seems to then run smoother. My mechanic said it was cylinder #2 but just switched the coils or something to see what would happen. It ran smooth for a while then became rough again. I took my truck in to dealer and they said I needed short block or something like that. My mechanic then changed out that one coil completely and it ran smooth for a while but once again is running rough. I am having all coils changed now, and will have him do wiring also. Spark plugs were changed earlier. My question is - does this sound like the picture for a truck that needs new/used engine block?
I have read the article on the misfiring and will have the mechanic look at those things mentioned; and I do not know what the diagnostic code was, but could get the info later.
(1) Answer
did your mechanic do a compression test?? this maybe the reason why the dealer told you a motor. the problem is that the diag is not complete until you do all the steps. i would get another opinion from another technician.