I’ve recently bought a 2004 rx8 with a rebuilt engine. (I’m new to the 8, but I’ve have an FC for about a year now.) The car sat for a couple months after being rebuilt, but not because of issues with the car. I started having intermittent issues a few days into ownership. At first it seemed to be a problem with the ignition system, based on info I’ve found through this site. I’ve since replaced all 4 coil packs, spark plugs, wires, and cleaned the MAF.
Some issues went away, but others have not.

The symptoms are as follows:
The car has suddenly shut off a few times, but always fires back up. I’ve never heard any noises when this happens. Several dash lights are illuminated with the battery light being the only one that lasts more than a couple seconds. None are visible while car is running.
It occasionally has a hard time starting when hot, but I don’t recall it happening since replacing the ignition system. When there is a problem it is usually solved by bumping the throttle a couple times.
The most common of the intermittent issues is that sometimes, when I’m driving, the car seems to lose power and sometimes stutters. It loses power at random rpms and only lasts a few minutes before the car runs good again.
When this happens, the car can not be revved, in neutral, with more than 1/4 to 1/2 throttle. If more accelerator is applied the cars revs bounce and it shuts off.
It stutters at while driving at speed and if press the gas pedal it kind of bogs and has no power.
It idles at a steady 800.
Keep in mind these aren’t everyday problems. They only seem to happen after the car has been running for more than a half hour or so.
I’m also throwing a CEL with no codes, but 3 failed monitors.
I’m getting terrible gas mileage, as well.
Through the research that I have done, I think it is a failing fuel pump. Although, I haven’t counted out the front 02 sensor or even a vacuum leak.

Any advise is appreciated. I’m going crazy trying to figure this out.

Modifications:
Mild street port
gutted cat
Aftermarket mufflers

2004 Mazda RX-8
6-speed manual transmission
147,000 miles on chassis, roughly 1,000 on rebuild.
New clutch, but it sounds like my release bearing is going out.
No compression test was done, as I was unable to acquire one before purchasing.(I’m going to have this done as soon as I can) The car hot and cold started perfectly, and did/does not smoke.

I have read the new owners section. That’s where I’ve acquired the information I have, and I’m still revisiting the section to find information I may have missed.

As previously stated the car has been hooked up to an OBD2 scanner. It showed ZERO/0 codes. Although, it had 3 incomplete monitors. It’s still throwing a CEL.

The catalytic converters is gutted.

I triple checked every plug and wire during install, and did them one at a time to minimize error. Though, I will recheck them to be 100% sure. Although, I’m no longer getting misfire codes or a flashing CEL.
The car runs perfectly 90% of the time, with no issues at any rpm. No issues starting hot or cold.
The problem seems to be significantly worse when there is under 1/4 tank of fuel. If I give it about 1/4 throttle when revving (when having issues) it revs perfect, if I give it more it either shuts off or bounces a couple times and revs through.
The gas mileage is probably around 12-15 in the city, and the engine has been mildly ported, after calculating mpg’s. It seems to burn more when having issues, though.
I’ve been out of town, so I haven’t had a chance to recheck some of these things, but it being my daily driver I need to fix these issues ASAP.
I’m going to upload a video of the issues to YouTube the next time it starts messing up, and post a link in this thread. I’m still doing research, but I figured it couldn’t hurt to ask, as well.

Im unsure of whether it’s been tuned or not. I’m assuming that it was at some point, but I know it was prior to the porting if it has been. I also know that it had previously passed NC State Inspection with it’s current mods, so it passed emissions somehow.

I just got ahold of an OBD2 pocket scanner, and it showed 2 codes. P0562, it showed that code twice. From what I’ve gathered so far I’m thinking that it’s my “room” fuse. I’m researching this issue further, as I’m typing this. (I’m pretty sure it’s getting blown by the factory radio).I just completely disconnected the radio, but have yet to be able to buy a fuse to replace it. So I won’t know for sure until tomorrow.

As far as the incomplete monitors it’s still showing 3.
-Catalyst
-02 sensor
-Evap

As well as 5 labeled as “ready”, but some of these were previously shown as “codes” before.
-Misfire
-Fuel
-Comp
-SecAir
-02 htr
I haven’t erased codes any of the times I’ve used an OBD2 scanner.
I’m really hoping this doesn’t mean that I’m losing compression, since the motor was just rebuilt.
It was idle hunting upon hot start a few minutes ago, but it cranked and fired without a problem. I blipped the throttle once and it idled perfectly and steadily afterwards and ran without a problem on the short drive home.
I thank you for your advise so far, and any given in the future. This isn’t my first rotary car, but is my first OBD2 car. So I’m at a slight learning curve when’s it comes to diagnoses.

It’s taken some time, but I think I’ve finally isolated the problem/s

The factory radio was the issue with the room fuse continuously blowing. I yanked it out, and the fuse hasn’t blown since.

It turns out that negative battery lead wasn’t fully taught. I tightened it down and the car now pulls through the rpm range with the throttle responding all the way to the floor. Previously it would sputter and then cut out at 5k past half throttle. It was showing 25% short term fuel trimat load, and showing a max of 45% engine load. Long term trims were around 6.25%.

One incomplete monitor is left, with that being evap. I have replaced the gas cap, but I am going to try to get a smoke test done to see if there are any leaks.

The car is hesitant around the mid rpm range, and the codes now being thrown are p2256, p2259, and P2010.
I’m going to check the Air Solenoid connector and wires as I’ve read that they are a leading cause for the 2259 code. I plan to check the APV valves and motor while doing this to try to remedy the 2010 code. I haven’t found anything on the 2256 code yet, but I think it’s the same cause as the 2259. (Correct me if I’m wrong).
I’m gaining some ground on having a great running car, slowly but surely.