So I’m having this issue on my partners 07 caliber that I’ve been trying to work out. That car started out losing power and throwing a multiple cylinder misfire on all cylinders. So far the spark plugs have been replaced and so has the downstream O2 sensor. Still having an issue and CEL comes on if you try to accelerate quickly and the engine clunks to try and go.

It’s now throwing codes:
P0339 - crankshaft position sensor intermittent
P0420 - catalyst efficiency below threshold (bank 1)
P0300 - multiple cylinder misfire

Could it be as easy as it needing a new crankshaft position sensor? I’m also thinking maybe the EGR needs to be replaced. I’ve read that there could be problems with the ECM which is new for me.

Looking for advice. Thanks