Questions for super experts (SES related)

[Paulpt]

Hi Guys,

I posted previously that my SES light was coming on, then off, then on, etc.

It finally came on and I was near an Autozone so I had it read. It gave the following:

P0505 - Idle control System malfunction
Po335 Crankshaft position sensor A circuit malfunction
Po368 Camshaft position sensor B bank one CKT intermittent.

No clue what these are but my questions are:

1- The car seems to run fine, a little sluggish in power (I bet the PO505 has something to do with it).
2- I have changed the plugs a few weeks back, can this have anything to do (replaced with OEM plugs).
3- Can one of these codes be activating the others?
4- Are any of these repairs DIY type?
5- Where would you start fixing? My experience is that sometimes a simple solution fixes the others, not sure in this case. Again the car is running OK I never had any issues really. Just these last couple of days if the SES light came on, I revved the car pretty high a couple of times, turned ignition off and then the light was off.

THIS IS FOR A 2001 X5 3.0 92K miles.

I hope this are not $$$$$ repairs and it is something I can manage myself (if it is replacing stuff).

Thanks in advance.

P