NB1 Miata Intermittent Codes...

Hey everyone! So a few months ago I got an 99' NB1 Miata that has been mostly problem free. I initially did all of the fluids+spark plugs and it's been running fine. It is not daily driven, just autocrossed 30 mins away. Lately I've been getting intermittent codes P0455 and P0704. One indicates an evap leak and the other is the clutch switch. I don't mind buying and replacing parts but I'm wondering why they're intermittent. Car runs fine and when I clear the codes they stay off for a bit but then they come back. I did some vague researching on the internet although I figured the GRM crowd could really set me straight here.

1) P0704 - Buy a new clutch switch, doesn't look too bad, unless maybe something is just loose?
2) P0455 - this one pretty much gave me super varied answers. Fuel cap, Fuel Pump Mounting Screws Loose, CDCV, etc.

There are no obvious things that are rotted/broken in the engine bay for what its worth. Just hoping someone with more experience with Miatas could give me some easy references so I don't end up buying the entire Miata catalog.

 I autocross my NB1 also, but my knowledge is a fraction of what is available here. They'll be along soon. 
 

I can submit that the clutch switches are an inexpensive and easy replacement, I would just do it. 
 

Do you smell gas in cabin or trunk? I have no idea if it will cause a code to save, but the fuel filler hose between the fender and the tank is something I've seen leak on a couple of Miatas. There's a smaller hose next to it. That is the drain hose for the well around the fuel fill. I would replace both as a pair.

If you send some event results, you can get a discount through Mazda motorsports as a racer. That can be handy for getting parts direct from Mazda at a discount. Here's the link.

Mazda team support program

I see you're in NJ. Because both codes are intermittent, I'd check the chassis grounds before I threw any money at the problem. 

https://forum.miata.net/vb/showthread.php?t=526247

Good tips. These fixes/items seem inexpensive and "easy" enough, will start there!

Here's the documentation. Shoot me an email at keith@flyinmiata.com and I'll send you the full diagnostic/repair procedure.

DTC

P0455

Evaporative emission control system malfunction (Con. leak detected)

DETECTION CONDITION

Fuel tank pressure measured immediately after purge control is stopped with canister drain cut valve closed is too high

POSSIBLE CAUSE

Purge solenoid valve malfunction

Canister drain cut valve malfunction

Tank pressure control valve malfunction

Vent cut valve malfunction

Loose fuel filler cup

Charcoal canister malfunction

Catch tank malfunction

Rollover valve malfunction

Cracked Fuel tank

Fuel tank component parts poorly installed

Evaporative hose damaged or loose

Insufficient manifold absolute pressure

EGR boost sensor malfunction

Fuel tank level sensor malfunction

Fuel tank pressure sensor malfunction

Engine coolant temperature sensor malfunction

Intake air temperature sensor malfunction

Throttle position sensor malfunction

Mass air flow sensor malfunction

Vehicle speed sensor malfunction

Open or short circuit in wiring harness

Poor connection of connector

Keith Tanner said:

Here's the documentation. Shoot me an email at keith@flyinmiata.com and I'll send you the full diagnostic/repair procedure.

DTC

P0455

Evaporative emission control system malfunction (Con. leak detected)

DETECTION CONDITION

Fuel tank pressure measured immediately after purge control is stopped with canister drain cut valve closed is too high

POSSIBLE CAUSE

Purge solenoid valve malfunction

Canister drain cut valve malfunction

Tank pressure control valve malfunction

Vent cut valve malfunction

Loose fuel filler cup

Charcoal canister malfunction

Catch tank malfunction

Rollover valve malfunction

Cracked Fuel tank

Fuel tank component parts poorly installed

Evaporative hose damaged or loose

Insufficient manifold absolute pressure

EGR boost sensor malfunction

Fuel tank level sensor malfunction

Fuel tank pressure sensor malfunction

Engine coolant temperature sensor malfunction

Intake air temperature sensor malfunction

Throttle position sensor malfunction

Mass air flow sensor malfunction

Vehicle speed sensor malfunction

Open or short circuit in wiring harness

Poor connection of connector

Whoa....that's a big list. Email sent.