Damp and wet conditions cause volvo 850 to misfire

P1310 is a misfire code which means misfire on more that one cylinder. Cat was probably damages as a result of the misfire. Start with replacement of the ignition cap, rotor, wires and plugs. could be another issue but most likely it is ignition 80-90% of the time

Since you changed parts, you have covered some possibilities. On the spark side, the Crankshaft sensor and( if equipped) the camshaft sensors give the information for the firing Pulse.

A wet connection on either part can certainly cause a misfire. There is also the possibility of a fuel injector misfiring due to a connection or bad ground on the injector during damp weather.

Sometimes if you get lucky you can see spark jumping on the motor by operating the engine in the dark. Mist the engine with a spray bottle of water to see if you can induce a misfire, if unsuccessful with normal weather conditions.

WD 40 often cures moisture problems.

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Get yourself a wiring diagram & start a logical
process- of learning about what your trying to repair

Your just simply playing around- with no idea of how things work

Diagnostic Test Code (DTC) P0302 has a generic description of "Cylinder Misfire - Cylinder Number 2".

A misfire simply means that when it came time for that cylinder to fire, it missed its chance.
There are many things that can cause a misfire. Some of the things are listed below. Diagnostics should be performed to eliminate the possible causes so you don't spend a lot of money replacing parts trying to "guess" what is causing it.

These are just SOME of the possible causes:

> Spark plugs
> Ignition cables
> Ignition coil
> Distributor cap (if equipped)
> Fuel injector
> Fuel injector circuits
> Burned engine valves
> Blown head gasket
> Cracked cylinder head
> Piston damage
> Cylinder block damage
> Broken valve springs
> Damaged camshaft
> Vacuum leaks

YOUR PLUG WIRES LEAKING OR IGNITION COIL PACK SOME HOW IS GETTING DAMP OR WET.

I'd be taking the dash apart looking for burnt wires in a harness, so you will likely have to take the outer cover off some of the bundles. Start tracing back from the plug in for the radio. Hope this helps.

This symptom is caused by a burned out blower motor resistor -- it needs replacing.

Check the distributor cap. It may have a fine crack in it allowing moisture in causing what u describe. Let me know how u make out.

Try cleaning the throttle body and air idle control valve (IAC). The computer kicks the idle up when the a/c is on, if your throttle body or AIC valve is full of crud it will idle very low and feel rough.

Spark plug wires may be the cause. for cold damp start issues water is a conducter and will send spark directly to an engine ground not through spark plugs. also look for oil in spark plug wells this can also cause a misfire under certain conditions.