Engine has a idle speed misfire and a strong smell of un burnt petrol

There's no code that says, "#3 spark plug" but there is a code P0303 which indicates a misfire has been detected on cylinder #3. That misfire could be due to a spark plug, but it could also be a bad spark plug wire or CoP, a bad fuel injector, bad injector wiring, burnt valve, etc. Changing the spark plugs and wires would likely be the easiest and one of least expensive places to start, especially if the truck is due for a tune up anyway, but if that doesn't fix it, consider the fuel injector next. Just because it idles fine does not mean that the spark is strong at higher engine speeds.

You might also want to clean your MAF sensor and check the linearity of your throttle position sensor (TPS) to make sure the stumble is not due to a bad spot in the TPS.

White smoke is water vapor and in this cold climate it is normal. Strong gas smell is not normal although you may smell some while engine is warming up. Bad cat converter can produce smells, but usually more like rotten eggs. If engine is running rough and seems rich, check coolant temp sensor. Bad converter can cause stalling too. Otherwise, idle speed is controlled by idle air contol motor which can get dirty and stick. Any codes set?

Check carefully for fuel leak. If it starts well and then gets worse as it warms up, check coolant temp sensor. May be it just smells like fuel because it misses so badly fuel is not being burnt and floods tailpipe. Check spark at plugs with timing light to avoid sparks where fuel may be present. Weak or irratic spark can be coil/module, crank/cam sensor. Remove plugs to see what they look like or which is not firing.

When your engine misfires fuel is still being pumped into the engine, it's just not being ignited. You need to find the cause of the misfire first. It could be: a bad sparkplug, a bad sparkplug wire, a leaking head gasket, a bad ignition coil, or cracked engine block. I'd start with the spark plugs first, then the ignition coils as they commonly fail. Good luck!

300 is a random multiple misfire meaning several cylinders are skipping its possible an exposed wire may have gotten wet causing a current disruption

I must say that was quite a bit of info for the first posting of which I am grateful. Most questions are 3 or 4 words if that.
I guess my first question is how does the engine perform now ?
Have you drove it since you got it back home ?
The biggest hassle of driveability problems is the need to recreate the event in the shop. If you can't make the problem happen on demand, it is all but impossible to diagnose.
I would want to know what the trouble codes were/are, what the fuel pressure is, and where the smell was coming from to proceed.
There is a long list of possible causes.

I would check your tps(Throttle positioning sensor) to see if its bad. That's what it sounds like.

you haven't said if its petrol or diesel so i'm assuming its petrol since your smelling sulfur sounds if you have a misfire causes could be plugs,leads or ign coil i suspect its ign coil these are common to go.

have you checked your air inlet manifold for any leakages by spraying WD40 around each portall bolted to the cylinderhead gasket,check for vacuum air pipes deterioration.make sure the engine is running first ,then spray WD40 to check that the engine speed should increase.it sounds like your engine is haveing problems breathing due to heavy hydro carbons increasing./and your CO2% is dropping.

Sounds like you may need to inspect and replace your fuel line from front to rear. no other reason for your problem.