First of all, the fault codes did not say to replace the ignition coils. They never say to replace parts. They only indicate the circuit or system that needs further diagnosis.
Second, if new coils didn't solve anything, the old ones should be reinstalled.
Third, a less expensive way to find the cause of the problem, if no one is going to actually diagnose it, is to swap parts instead of replace them. For example, if cylinder # 2 has a misfire code, swap its injector with the one from cylinder # 3. Swap the spark plug with the one from cylinder # 6, (even if it is new), and swap the ignition coil with the one from cylinder # 7. Now you go out and drive it until the misfire is detected, then see which cylinder it is. If the misfire is still on cylinder # 2, suspect a compression problem.
Misfires are no more common on your engine than on any other brand, and I don't even know which engine you have. Any issue you can think of on any brand of vehicle is going to have a lot of posts on the internet. That doesn't mean it's common. What you WILL find are the common solutions. All engines use the same parts and have the same breakdowns, so of course they will have the same solutions. Some of those solutions that we take for granted may not be common to YOU though, and that's where the forums can be helpful.
The first mechanic made the right guess as spark plugs and wires are the most common causes of misfires, and obviously they solved the problem, ... At least it appeared to. Unless you were not near that first mechanic, the second trip should have been to the same person because deserves a chance to recheck his work, and he knows the recent history. From your description I am not too sure I trust the second mechanic's judgement. A failed crankshaft position sensor will cause the engine to stall. Except for extremely unusual circumstances, it will not cause just one or two cylinders to misfire. There may have been something he saw with the PCV valve, but that is also not related.
Since you already have new injectors, coils, and spark plugs, start with a compression test.
Please consider a to help us answer more questions.
Tuesday, February 26th, 2013 AT 9:24 PM