Two days ago my volvo 850 failed to start. When the key is turned in the ignition to lights turned on and it seems to get ready to start but it doesn't seem to catch and fails to start.

The night before it had rained quite a bit. I'm not sure if that has any affect on the spark plugs. Today I had turned it on and finally it started.

However I can hear a faint clicking noise coming from the engine as it runs and no longer seems as powerful.

White smoke has also started to come out of the muffler and this is something that has never happened before.

On a side note. The PCV system does need to be changed but I'm not completely sure if it is the reason this is happening. Besides replacing the system itself are there any other components that should be replaced along with it?

I'm at 175,000 miles. Should the spark plugs, distributor, and wires be replaced as well?

Thanks.

 

The recommendations will vary depending on if you go by Car Mfg, part company or mechanics. In general, the plugs should be done at 25 to 30K intervals if you're using standard plugs, and the wires, distributor cap and rotor should be done with the plugs or every other. This is preventative maintenance and like I said it isn't cut in stone as different people will recommend different intervals.
As for your car, when were they done last ??
If you don't know, replace them and keep a record of maintenance.
You are having a performance issue so I'd replace the wires at least.
The plug wires can be tested with an ohm meter to determine if they are internally good but it won't tell you if the insulation is cracked from age and physical wear and tear and shorting to ground. You might be hearing a snapping from the spark jumping to ground from a broken wire or two instead of getting to the spark plug and firing the cylinder. It's worse when it's wet outside. The higher humidity allows the wires to short easier.
Start it up at night and open the hood and look to see if you can see any arching. The other trick mechanics use is to have a spray bottle with water in it and mist the wires to see if they short. DO NOT use a garden hose. Had one clown do that and drown his engine. Just a spray bottle and mist them. If they are bad you should hear the snap and can see a spark jump.