Noob here, I just bought one of these beautiful cars, but wouldn't you know it came with engine troubles. Imagine that.It is a 2004 model with 76k miles and has the automatic transmission. I have read at least 30 threads and although many people seem to have very similar issues, I haven't been confident that anyone has an exact match for my particular issue.

As I said, I have looked at dozens of these threads and other sources as well, and it looks like it could be coil packs, spark plugs, plug wires, back cat, vacuum leak(s), various air/fuel ratio sensors related or, heaven forbid, a blown engine. I was hoping to get opinions on what some more experienced rx8 owners think. Also, in what order would you troubleshoot?

1. Car will absolutely not start when warm.
2. Severe lack of power until up to 4k rpms.
3. Idles rough but somewhat steady @ a little under 1k rpms but not as badly as some I've read about here.
4. Check engine light has been on since I bought it a couple of weeks ago. 2 codes were given: both were P0300, multiple misfires detected.
5. Brand new K&M intake
6. Alleged new coil packs (will be looking here first just to confirm this)
7. When I first bought the car, I drove "pretty aggressively" on the interstate on the way home. I got it up to about 90 @ about 6k rpms before it stopped accelerating and the check engine light started flashing . It didn't die or anything, but it just seemed to have not let me go any faster but would maintain that speed.

I am somewhat handy with turning wrenches and am going to do my very best to DIY this thing, but I have several questions and any other insight you guys might have. Is there a more relevant thread I missed? In what order would you try to diagnose the issue? If I drilled a hole through the back cat with a drill bit on a long, flexible extension, would it fix the issue if it's the back cat? And if I did drill it, exactly how much louder would the exhaust be?

I appreciate anything you guys contribute to this thread. Although I have always loved these cars, I didn't want to get it under the circumstances in which I got it. But I have a family and they have to go places. Also, even though I hastily purchased my car, it doesn't mean I can't make it the nicest car I've ever had.

 

Welcome. I guess no compression test before purchase?

Sounds like clogged catalytic converter caused by poor ignition health and leading to engine failure. Pretty classic unfortunately.

Get a comp test if you can, you can confirm/deny the diagnosis and make your decisions from there. Did it have all these symptoms during your test drive?

Why did you drill through the cat? That's not exactly a repair procedure.

 

I didn’t get a compression test before I bought it. I did probably an hour of research before I test drove it and it looked like (and still may very well be a coil or cat issue.) I got the car for dirt cheap andd am interested in fixing it up because as I said, I’ve always liked rx8s. I will be conducting a compression test tomorrow using the video method.

I haven’t drilled the cat… yet. I’m working out of town right now and would really like to get it on the road. If drilling it will not be a catalyst (see what I did there?) for some sort of catastrophe, would it hurt until I received a new one?

 

If you are using the video tape method, you also need a way to get your cranking RPM through OBD2. Important because rotary compression changes with cranking RPM and you will need to correct it with this info.

Otherwise, your cats may not necessarily be bad. Does it visually look clogged? You can use a flashlight to determine that. Removing cats don't harm your car, but it will smell horrendous and you won't be passing inspections.

Don't forget to test the spark plugs and ignition coils with a timing light.

 

Don't drill through $2000 parts that aren't confirmed dead
Take it down, inspect it, decide from there.

 

So, I performed the compression test yesterday, albeit without the modifications you recommended. Compression was not too bad (740.09 kPa @ 204rpm) and absolutely identical. Now she won't start. Starter's good and didn't used to have trouble cold starting. Didn't hit the gas but could it still be flooded? I did alsk confirm today that I didn't cross plug wires.
I also confirmed that the plugs, plug wires, and coil packs are all, indeed, new. However, the coil pack boxes did look like an Amazon special.
I'd really like some help here as far as testing sensors, etc. I will listen but may not always have the money to put racing components on it (oh, to drop a 20b in), but I do like these cars and want to learn about them.
What would be your next move?
And how would I know the cat was clogged by looking in the tailpipe?

 

At the end of the day engines are all the same. This engine works differently but it still needs to intake air and fuel mixture, then needs compression (which you now know you have), create spark, then exhaust the gasses out. Could be a fuel pressure issue, could be an intake issue and could be an exhaust issue. I cant see the car in person so all I can really do from here is advise. But these are the areas you need to investigate if you know that it has compression. Did you try the deflood procedure? Possible it could just be flooded after you tested it due to an issue with something else.

Edit: when you take the cat down, look for cracks and discoloration. You cant see anything from the tailpipe, it needs to be physically removed from the car.