Code P0171 I, check engine light car is idling rough?

So the system thinks the exhaust is lean, so it wants to add fuel, this is why you get the smell. This can be caused by the engine misfiring, or you have a leaky fuel injector which would cause double trouble (misfire and stinky exhaust).

P0171 - System Too Lean (Bank 1)

I would go over these guides, both will help you understand what is going on. Then I would remove the spark plugs and look for one that is black, this will be the cylinder that is having the issue.

https://www.2carpros.com/articles/repair-lean-mixture-codes-p0171-or-p0174-on-some-manufacturers

Does your engine have an exhaust leak? This can cause the computer to run rich.

https://www.2carpros.com/articles/engine-misfires-or-runs-rough

This goes over the reasons for a misfire, but I can walk you through the steps to fix it if you get back to me on the spark plug condition. Check out the images (below). Please upload pictures or videos in your response.

This code po171 is to indicate that there's a lean condition here's a list of a few things that can cause this condition
1.A vacuum leak. Chech all hoses boots ect to see if any are disconnected or cracked. Split or damaged leaking.
2.A leaky intake manifold or other related components.
3.A leaky brake booster or booster hose.
4.A bad MAF sensor
5. A bad o2 sensor
6.A fuel system problem

"Good luck hope this helps ".

Yep its a pretty easy fix. Most likely the coolant is spraying out and dripping down onto the cat and the rest of the hot components down there thats where the smell would be coming from its burning the coolant off might smell a little sweet but that should go away onece you replace that hose and that should be done right away without hesitation and I wouldnt drive the car anymore till its repaired on that note the good thing is while youre doing it you might find some of the other things I meantiined since you be up close in there for a few mins. Hope this helps "good luck "