Troubleshooting unusual AFR's
 

So I turbo'd my Miata over the summer, running a MS2 PNP and did most of the tuning myself. I had the fuel map dialed in great and hadn't touched it for the last month or so, but that went out the door yesterday.

I was forced to drive 2hrs in the cold rain and when I got back, I realized my idle AFRs were way high. Usually, they would sit ~14.5, but as of today, they are sitting ~19 consistently even after multiple drives. Idle is where the AFRs are elevated the most, but they are raised through the whole map. However, it will get down to ~11 at full throttle.

The issue is not with the sensor since there is hesitation and rough idle now. I guess I could retune the whole map for more fuel, but I'm really trying to figure out how a drive in the rain could cause less fuel to flow... Don't want to put a bandaid on a bigger problem.

Any ideas on where I should even start troubleshooting? This one's got me pretty stumped

Alternator belt slipping? What is the battery voltage when this is happening?

That's actually a great deduction I wouldn't have thought of... However, I just pulled up Tuner Studio to check and saw that the IAT sensor was reading 212F intake temps... Looks like the water somehow fouled the plug connection since it's tapped into the IC side tank near the wheel well.

Unplugged it, readings went to the standard 70F, and AFR's dropped to ~15.5. Still not where it used to be, but I believe that was the main issue. Looks like ill have to order a new IAT sensor and add more water protection.