Yesterday I was driving in second gear and about to shift up to third. Next thing I hear is a loud grumbling noise which was very deep. My power went down dramatically and a blinking cel came on. I tried to slighlty accelerate to a safe spot on the road and the car was unresponsive. I begane to roll down a hill and my breaks were extremely resistent and tough to depress. I shut the car off and waited for a little while then tried to refire. It sounded like it was misfiring and when the car started it would not properly idle at the normal level and did not sound anywhere near how it should. I had my car towed to the AAA a block away and they informed me that they read out the cel for p0300 and p0171. They informed me of rattling, a slight crackling or popping sound, and also said that my car was supposed to have been recalled for pcm reprogramming.

Has anyone ever dealt with this. I'm really worried that this may be a fatal problem. My car has 64k miles and is an 04.

Those are misfire and system running lean codes.
I had the same loud grumbling sound when my MAF got hit with water.
I would start with cleaning that first.

Also, when was the last time you changed the spark plugs and coils?

jon,
My spark plugs were replace about 1.5 years ago. am not sure the last time the coils were.
As far as the grumbling, I do not know where water would have came from for me. I contacted the mazda dealership and they said that it was most likely my Cat. Would a cat problem cause all of those symptoms? I am still under the emission warranty but wonder if a intake would be enough to void that.

It can possibly be the cat.
If they replace it under warranty, thats good for you weather or not it was the culprit.

Not saying water got in your intake and hit the MAF, I'm just saying that an inaccurate reading from the MAF could cause that kind of sound.
This is why I suggested cleaning it. Plus its simple to do.
Plus with you having an '04, that year has its oil filler neck routed to the intake.
So its possible that oil residue could have built-up on the wires.