Take the panel off from under the steering wheel first. This will give you access to the pedal. You'll also have to remove the plastic heating duct. While you're at it, check and possible replace the rubber stopper contacting the clutch cut switch. The switch makes contact with the rubber stopper and the rubber stopper usually breaks over time. The rubber stopper is located where "A" is referenced in the picture above. "B" is where the clutch cut switch is located. The stopper itself is green. If you're missing one, you need to replace it.
The part number through Mazda is B001-43-029. There is also a part number G030-43-029. This probably has to do with the year and whether or not you have C/C.
I just did the same thing yesterday but I haven't replaced the rubber stopper yet. I took it off and replaced it with a Home Depot stopper for the time being. The clutch switch is VERY important and it is very important that that stopper (or A stopper) be put in place. The clutch switch plays an important role in deceleration, detection of car in gear, fuel injection amount, ISC valve, as well as the igniter itself. If your car is running like crap, it could be as simple as this rubber stopper missing.
Here is what's left of mine from yesterday:
My car started acting funny on decel a couple weeks ago and I found the other half of the green stopper on the floor. It had also started backfiring at certain times. I went over the ignition and changed my timing, it still did it. I adjusted my clutch pushrod yesterday and noticed that half the stopper was missing. I went to Home Depot and bought some plastic stoppers with adhesive backing (used for furniture legs so you can slide furniture without ruining the carpet)
I found one that was the same thickness as the rubber stopper and put it in place on the clutch arm. The clutch switch is now making full contact with the arm when the3 clutch is engaged. All decel problems have gone away and no more backfiring. The switch was only making contact with part of the stopper at certain points and none at other times. The rubber stopper was able to swivel around. This made the switch make contact at some points, but other times it made contact later than it should have. This with shifting was what was causing the backfiring and problems on decel.
I may or may not order the rubber stoppers from Mazda. Both part numbers are correct but I have never ordered them before. Either way, they can't cost all that much so it would make sense to just order both and use which one is the correct number. I can't imagine them being more than $2.00-$3.00 a piece.